Mosquito abundance and distribution
In 2018, one to three months before the 2018 MDA, an MX survey was conducted in 28 randomly selected PSUs on the two main islands of Samoa (Upolu and Savai’i). A total of 8,506 female mosquitoes were trapped, with a mean of 320 per PSU (range 147-781, median 278). Culex were the predominant category (n=4,333, 48%), followed by Aedes polynesiensis (n=2,498, 28%), other Aedes spp. (n=1,443, 16%) and Ae. (Finlaya) spp. (n=698, 8%) (Supplementary Table S1). The predominant species in the Culex and Aedes (other) categories were Cx. quinquefasciatus and Ae. aegypti, respectively. Numbers of Ae. polynesiensis by PSU ranged from 9 to 248 (mean 89, median 69) (Fig. 1a). Summaries for other species are available in Supplementary Table S1.
In 2019, six to nine months after the 2018 MDA, a repeat MX survey was conducted in Upolu, Savai’i, and Manono islands across 35 PSUs (30 randomly selected and five purposively selected because of high Ag prevalence in previous human surveys). A total of 34,299 female mosquitoes were trapped, with a mean of 980 per PSU (range 290-3,719, median 855). Cx. quinquefasciatus was the predominant species (n=17,807, 52%), followed by Ae. polynesiensis (n=10,540, 31%), Ae. aegypti. (n=3396, 10%) and Ae. (Finlaya) spp. (n=1377, 4%) (Supplementary Table S2). Numbers of Ae. polynesiensis varied by PSU with a range of 22 to 1,046 (mean 301, median 173) (Fig. 1b). Summaries for other species are available in Supplementary Table S2.
Estimated prevalence of LF infection in mosquitoes
In 2018, mosquitoes were sorted into 475 pools (mean 18 mosquitoes/pool, range 1-25); 18% of pools were positive for W. bancrofti DNA by PCR. The highest positivity rate of pools was in Aedes spp. (other) (30%), followed by Ae. polynesiensis (24%) (Table 1). Overall estimated infection prevalence in all species combined was 0.9% (95% credible interval [Crl] 0.2-2.3), with the highest prevalence in Aedes spp. (other) (1.6%) followed by Ae. polynesiensis (1.2%). Highest prevalence was found in Northwest Upolu (NWU), north-east coast of Upolu (Musumusu and Faleapuna) and southeast Savai’i (Papa & Tafua) (Fig. 2a, Supplementary Table S3).
<p>In 2019, mosquitoes were sorted into 2,638 pools (mean 13 mosquitoes/pool, range 1-25). Most pools consisted of <em>Cx. quinquefasciatus</em> (39%) or <em>Ae. polynesiensis</em> (27%). In total, 7% of pools were PCR-positive. The highest positivity rate of pools was in <em>Ae. polynesiensis</em> (14%), followed by <em>Ae. aegypti</em> (7%) (Table <span class="InternalRef">1</span>). Estimated infection prevalence in all species combined was 0.3% (95% CrI 0.05-1.0%), with the highest prevalence in <em>Ae. polynesiensis</em> (0.6%). Highest prevalence was observed in NWU within three purposively chosen PSUs not sampled in 2018: Lauli’i (7.5%), Fasito’o Tai (7.1%) and Faleasiu (6.4%) (Fig. <span class="InternalRef">2</span>b, Supplementary Table S4).</p>
<div class="Section3" id="Sec6">
<div class="gridtable">
<table border="1" style="border: none; border-collapse: collapse; empty-cells: show; max-width: 100%;">
<caption language="En">
<div class="CaptionNumber">Table 1</div>
<div class="CaptionContent">
<p style="margin-bottom: 10px !important;">Detection of <em>W. bancrofti</em> DNA in female mosquito pools in 2018 (28 PSUs) and 2019 (35 PSUs) in Samoa. Results for 2019 are spilt by randomly (R) or purposively (P) selected PSUs. Purposive PSUs were not surveyed in 2018.</p>
</div>
</caption>
<tbody>
<tr style="user-select: none;">
<td align="left" rowspan="2" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">Year</p>
</td>
<td align="left" rowspan="2" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">Species category</p>
</td>
<td align="left" colspan="2" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">Females (n)</p>
</td>
<td align="left" colspan="2" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">Pools (n)</p>
</td>
<td align="left" colspan="2" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">Positive Pools (n)</p>
</td>
<td align="left" colspan="2" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">Positive pool (%)</p>
</td>
<td align="left" colspan="2" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">Estimated infection prevalence* (%)</p>
<p style="margin-bottom: 10px !important;">(95% Crl)</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">R</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">P</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">R</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">P</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">R</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">P</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">R</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">P</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">R</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">P</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" rowspan="5" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">2018</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Ae. polynesiensis</em></p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">2451</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">136</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">33</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">24.3</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1.2</p>
<p style="margin-bottom: 10px !important;">(0.3-2.9)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Ae. (Finlaya)</em> spp.</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">219</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">33</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">3.0</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.4</p>
<p style="margin-bottom: 10px !important;">(0-1.6)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Aedes</em> spp. (other, including <em>aegypti)</em></p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1866</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">105</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">31</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">29.5</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1.6</p>
<p style="margin-bottom: 10px !important;">(0.4-4.1)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Culex</em> spp. (all)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">3970</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">201</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">21</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">10</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.4</p>
<p style="margin-bottom: 10px !important;">(0.1-1.0)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">All species</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">8506</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">475</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">86</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">18.1</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.9</p>
<p style="margin-bottom: 10px !important;">(0.2-2.3)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">NA</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" rowspan="8" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">2019</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Ae. polynesiensis</em></p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">8,833</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1,703</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">612</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">111</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">56</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">46</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">9.2</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">41.4</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.6</p>
<p style="margin-bottom: 10px !important;">(0.1-2.4)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1.8</p>
<p style="margin-bottom: 10px !important;">(0.2-6.9)</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Ae. (Finlaya)</em> spp.</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1,232</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">145</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">170</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">28</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.6</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">3.6</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.2</p>
<p style="margin-bottom: 10px !important;">(0-0.8)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.5</p>
<p style="margin-bottom: 10px !important;">(0-2.6)</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Ae. aegypti</em></p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">2,861</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">535</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">399</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">70</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">26</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">7</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">6.5</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">10</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.5</p>
<p style="margin-bottom: 10px !important;">(0.1-2)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1.5</p>
<p style="margin-bottom: 10px !important;">(0.1-5.6)</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Aedes</em> spp. (all other)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1,002</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">134</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">169</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">36</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">4</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">3</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">2.4</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">8.3</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.5</p>
<p style="margin-bottom: 10px !important;">(0-1.7)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1.8</p>
<p style="margin-bottom: 10px !important;">(0.1-4.9)</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Cx. quinquefasciatus</em></p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">16,448</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1,359</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">917</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">100</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">25</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">3</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">2.7</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">3</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.1</p>
<p style="margin-bottom: 10px !important;">(0-0.4)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.3</p>
<p style="margin-bottom: 10px !important;">(0-1.2)</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;"><em>Culex</em> spp. (other)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">23</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">8</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
<p style="margin-bottom: 10px !important;">(0-0)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0-0</p>
<p style="margin-bottom: 10px !important;">(0-1)</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">Unidentified</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">15</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">4</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">14</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">3</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
<p style="margin-bottom: 10px !important;">(0-0)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0</p>
<p style="margin-bottom: 10px !important;">(0-0)</p>
</td>
</tr>
<tr style="user-select: none;">
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">All species</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">30,414</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">3,881</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">2,289</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">349</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">112</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">60</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">4.9</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">17.2</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">0.3 (0.05-1.0)</p>
</td>
<td align="left" style="min-width: 5px; border: 1px solid rgb(221, 221, 221); user-select: text;">
<p style="margin-bottom: 10px !important;">1.1 (0.1-3.9)</p>
</td>
</tr>
</tbody>
</table>
</div>
<p style="margin-bottom: 10px !important;"><br style="color: rgb(0, 0, 0); font-family: Times; font-size: medium; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"></p>
<div class="Section4" id="Sec7">
<p><strong>Comparison between mosquito infection prevalence in randomly vs purposively selected PSUs in 2019.</strong></p>
<p>In 2019, crude infection prevalence in all mosquito species in randomly selected PSUs was 0.30% (95% CrI 0.05-1.05%), lower than the 1.1% (95% CrI 0.1-3.9%) in purposively selected PSUs. This difference remained statistically significant after adjusting for mosquito species, region, and clustering within PSUs (OR: 0.24, 95% CrI 0.06-0.86). For both randomly and purposively selected PSUs, the highest prevalence was observed in <em>Ae. polynesiensis</em> (0.6% and 1.8% respectively), followed by <em>Ae. aegypti</em> (0.5% and 1.5% respectively).</p>
<p>For the 28 PSUs that were sampled in both years, estimated mosquito infection prevalence for the country was higher in 2018 than 2019 for both the entire sample (‘any species’) (0.9% vs 0.3%) and <em>Ae. polynesiensis</em> (1.2% vs 0.5%). This decreasing trend was observed across all species categories nationally and in all regions, although not all differences were statistically significant (Fig. <span class="InternalRef">3</span>, Supplementary Table S5).</p>
</div>
</div>
<div class="Section3" id="Sec8">
<p>After adjusting for mosquito species and clustering within PSUs, infection prevalence at the national level was lower in 2019 than 2018 (odds ratio [OR] 0.4, 95% CrI 0.2-0.6) and in three regions (NWU: OR 0.6 [95% Crl 0.4-0.9], ROU: OR 0.1 [95% Crl 0-0.2], SAV: OR 0.3 [95% CrI 0.1-0.8]). Estimated prevalence declined in AUA, but the difference was not statistically significant (OR 0.6, 95% CrI 0.2-1.5). Given the low prevalence, these ORs closely approximate prevalence ratios. For example, infection prevalence in mosquitoes in ROU was ~90% (i.e. 1 – 0.1) lower in 2019 than in 2018. This trend was seen across all PSUs, but only statistically significant in 10 PSUs (Supplementary Table S6).</p>
<p>In 2018, 50% (14/28) of PSUs contained at least one PCR-positive pool of <em>Ae. polynesiensis</em> and 82% (23/28) contained at least one PCR-positive pool of ‘any species’. Results were similar in 2019, with 63% (22/35) of PSUs returning at least one PCR-positive pool of <em>Ae. polynesiensis</em> in 2018 and 80% (28/35) returning at least one PCR-positive pool of ‘any species’ (Fig. <span class="InternalRef">4</span>).</p>
</div>
Human Ag and Mf infection
In 2018, we recruited 1542 participants aged 5-9 years and 1551 participants aged ≥10 years from 30 randomly selected PSUs. In 2019, we recruited 1811 participants aged 5-9 years and 1815 participants aged ≥10 years from the same 30 PSUs. The numbers of participants in 2018 and 2019 in each of the four regions are given in Supplementary Table S7 and Supplementary Table S8 respectively. Nationally, age-adjusted Ag prevalence in the 6-9 months post-MDA was similar in 2018 and 2019 (Fig. 5). Results at the regional level were mixed, with two regions (NWU and SAV) showing an increase from 2018 to 2019 in both age groups. Only one region (AUA) showed a decrease in Ag prevalence in 2019 in both age groups.
In 2018, 13 Mf-positive participants were identified in the 30 randomly selected PSUs, and 10 out of these 30 PSUs (33.3%) had at least one Mf-positive participant. Prevalence of Mf infection was likely underestimated in 2018, because the survey was conducted after MDA 13. In 2019, 17 Mf-positive participants were identified in the same 30 random PSUs and at least one Mf-positive participant was found in 10 of the 30 PSUs (33.3%), but not in the same 10 PSUs as 2018. Six PSUs had Mf-positive people both years, four PSUs only in 2018, and four PSUs only in 2019. Fourteen PSUs (46.7%) had an Mf-positive person one or both years.
Presence of PCR-Positive pools as indicator of Ag-positive humans in a PSU
At the PSU level, there was no significant association between the presence of Ag-positive humans and PCR-positive mosquito pools in 2018 or 2019, whether considering all mosquito species (Fisher exact p-value 0.73 in 2018; 0.83 in 2019), all Aedes (Fisher exact p-value 0.89 in 2018; 0.73 in 2019), or Ae. polynesiensis only (Fisher exact p-value 0.68 in 2018; 0.52 in 2019). Consequently, the sensitivity, specificity, positive predictive value, and negative predictive value of PCR-positive pools to identify Ag-positive PSUs were no better than random classification (Supplementary Table S9). However, combining MX (all species) and Ag surveillance of humans identified more positive PSUs (those with positive humans and/or mosquitoes detected) than each method alone, with 96% (27/28) of PSUs being positive for MX (all species) and/or Ag in 2018 and 97% (34/35) in 2019. Ag surveillance used alone identified 79% (22/28) in 2018 and 80% (28/35) in 2019. For MX, using ‘all species’ identified the most positive PSUs with 82% (23/35) in 2018 and 80% (28/35) in 2019, followed by ‘all Aedes’ with 75% (21/28) in 2018 and 69% (24/35) in 2019, and Ae. polynesiensis with 50% (14/28) and 63% (22/35) in 2019 (Fig. 6).
Detecting a change in human or mosquito infection prevalence post-MDA
Mapping the results from Fig. 6 by PSU shows the spatial distribution of MX and human Ag (and Mf) results (Fig. 7). PCR-positive mosquitoes and Ag-positive humans were found in all regions in both years. In 2018, of the 23 PSUs with PCR-positive pools, nine (39%) did not return any positive Ae. polynesiensis pools; in 2019, this proportion reduced to 21% (six out of 28 PSUs).
Figure 8 represents the change in mosquito infection or human Ag prevalence between 2018 and 2019, expressed as ORs where an OR of one indicates no change, OR <1 a reduction, and OR of >1 an increase in prevalence. MX showed a significant reduction in mosquito infection prevalence from 2018 to 2019 nationally and in all regions for ‘all species’ and Ae. polynesiensis. There was no significant change in Ag prevalence in participants aged ≥10 years or 5-9 years at the national level. Variable patterns were observed at the region level, with a significant increase in Ag prevalence between 2018 and 2019 in 5-9 year-olds in NWU and in ≥10 year-olds in SAV, but a significant decrease in ≥10 year-olds in AUA.