Descriptive epidemiology
Between 1 June and 30 September 2017, we found 81 cases (75 probable and 6 confirmed) in the tri-district area, with four deaths (case fatality rate=4.9%). Of these cases, 55 were from Lyantonde, 16 from Rakai, and 10 from Lwengo District. Common symptoms included fever (100%), rash (100%), coryza (96%), cough (92%), and conjunctivitis (91%).
Among those that died, there was one female and 3 males, aged 11 – 17 months. Only one case that died had history of one dose measles vaccination. The major cause of death was respiratory complications (3/4) and the cause of death could not be ascertained for one of the cases. All the cases that died were managed at home for the measles virus infection. In addition 3 of those cases had other underlying disease conditions.
The initial cases had rash onset on 21 June. Cases started to increase in July and August, and the last case occurred on 12 September. The epidemic curve was indicative of a propagated outbreak. An emergency mass vaccination was rolled out in the tri-district area. This involved health facility based mass vaccination campaign for all children below 5 years of age. (Figure 1).
Of all age groups, children aged 9 months–5 years (AR=32/100,000) and those 4-9 months (AR=17/100,000) were the most affected. Females (AR = 9.4/100,000) and males (AR=8.1/100,000) were similarly affected (Table 1).
Table 1: Measles attack rate by age and sex during an outbreak: Lyantonde, Lwengo and Rakai districts, June–September 2017
Characteristics
|
Population
|
Num. of cases
|
AR (/100,000)
|
Overall (three districts)
|
926000
|
81
|
8.7
|
District
|
|
|
|
Lyantonde
|
101200
|
55
|
54
|
Rakai
|
543400
|
16
|
2.9
|
Lwengo
|
281400
|
10
|
3.6
|
Age group
|
|
|
|
<9m
|
35610
|
6
|
17
|
9m–5y
|
158320
|
50
|
32
|
6–18y
|
336930
|
21
|
06.2
|
≥18y
|
395140
|
4
|
1.01
|
Sex
|
|
|
|
Male
|
457100
|
37
|
8.1
|
Female
|
468900
|
44
|
9.4
|
The attack rate in the tri-district area was 8.7/100,000. The initial cases in June occurred in Rakai District. The outbreak started to affect Lyantonde District in July, and later spread to villages in Lwengo District bordering Lyantonde District. Lyantonde District had the highest AR (54/100,000) of all 3 districts (with 68% of all cases). Within Lyantonde District, Lyantonde Rural Sub-county was the most affected (AR=16/10,000) (Figure 2).
Findings from the hypothesis generation interviews
Of the 15 probable measles case-patients interviewed, 67% reported having visited Lyantonde Hospital during the 3 weeks before onset of symptoms; 40% of the patients reported having gone to school, 20% had visitors with measles at home, 20% went to a church, and 13% went to communal water-collection points; 73% of the case-patients had no history of measles vaccination.
Case-control study findings, VC, and VE
In the case-control study, case-patients and controls were comparable in mean age (6.0 years among case-patients vs. 5.9 years among controls) and sex distribution (41% of case-patients and 42% of controls were males). During the bivariate analysis, 44% of case-patients and 2.3% of controls had been hospitalized in the pediatric department of Lyantonde Hospital for non-measles conditions 7-21 days before case-patients’ rash onset (OR=30, 95% CI: 7.0-132). Visiting any health facility 7-12 days before case-patient’s rash onset was a significant risk factor. Going to church and going to communal water collection points were inversely associated with illness. In the final conditional logistic regression model, hospitalization at the pediatric department (ORadj=34, 95%CI: 5.1-225), going to communal water collection points (ORadj=0.056, 95%CI: 0.0066-0.47) and measles vaccination history (ORadj=0.051, 95%CI: 0.011-0.25) remained significant. All vaccinated cases and controls reported received at least one dose of measles vaccine. The associations of measles with other risk factors became non-significant (Table 2).
Table 2: Association between measles and exposures during an outbreak: Lyantonde, Lwengo and Rakai districts, Uganda, June–September 2017
Exposure*
|
% cases
(n=34)
|
% controls
(n=136)
|
OR † (95% CI)
|
ORadj‡ (95% CI)
|
Exposures during case-patient’s likely exposure period§
|
|
|
|
|
Hospitalized at pediatric department, Lyantonde Hospital
|
47
|
2.3
|
30 (7.0-132)
|
34 (5.1-225)
|
Visited any health facility
|
59
|
36
|
2.6 (1.2-5.5)
|
|
Went to communal water point
|
12
|
39
|
0.14 (0.039-0.51)
|
0.056 (0.0066-0.47)
|
Went to church
|
38
|
61
|
0.36 (0.16-0.81)
|
|
Went to school
|
47
|
41
|
1.4 (0.55-3.6)
|
|
History of measles vaccination
|
26
|
76
|
0.11 (0.043-0.27)
|
0.051 (0.011-0.25)
|
* Some records had missing values for exposure variables, including 4 for “hospitalized at pediatric department, Lyantonde Hospital”, 1 for “went to communal water point”, 2 for “went to church”, and 2 for “went to school”. These records were excluded from the respective analysis.
† OR=Crude odds ratios from univariate conditional logistic regression analysis, in which the matching variable was the case-control set.
‡ ORadj=Odds ratios from multivariable conditional logistic regression.
§ Case-patient’s likely exposure period = 7-21 days (minimum-to-maximum incubation periods) before case-patient’s rash onset.
The estimated VE was 95% (95% CI: 75-99%). The estimated VC, based on the percent of controls that had a history of measles vaccination, was 76% overall, and did not differ greatly between age groups (Table 3). The estimated VC based on administrative data for Lyantonde District was 83%.
Table 3: Measles vaccination coverage by age during an outbreak: Lyantonde, Lwengo and Rakai districts, Uganda, June–September 2017
Age (years)
|
Vaccination Coverage (%)*
|
95% CI
|
Overall
|
76 (101/134)
|
68-82
|
9 – 12 months
|
86(12/14)
|
52-98
|
9months-5y
|
72 (64/90)
|
62-80
|
6-18y
|
77(29/38)
|
60-89
|
>18y
|
83(5/6)
|
41-99
|
* Estimated based on the percent of controls in the case-control study who have been vaccinated.
Assessment of the pediatric department at Lyantonde Hospital
The pediatric department at Lyantonde Hospital had 2 wards. Initially, measles patients and other patients were mixed in the same wards because the measles diagnoses had not been made. After the measles outbreak was confirmed based on results from Uganda Virus Research Institute, the hospital attempted to put non-measles patients into Ward 1 and suspected measles patients into Ward 2. However, the 2 wards were adjacent to each other and only separated by a half-constructed wall; air moved freely between the 2 wards. Moreover, when Ward 1 exceeded its capacity, some non-measles patients were transferred into Ward 2. Windows of both wards were kept closed. Later during the outbreak, a windowless “isolation room” was set up to hold critical measles patients. The “isolation room” was at the extreme end of the pediatric department; patients had to pass through the whole department to access this room, allowing measles and non-measles patients to mix (Figure 3). During our environmental assessment, we observed free mixing of measles and non-measles patients in the reception area.