COVID-19 test positivity rate dynamics in West Sumatra, Indonesia: a retrospective study

Background: COVID-19 test positivity rate (TPR) is essential to estimate and control SARS-CoV-2 transmission in a population at a specic time, yet the TPR trends at a provincial level in Indonesia are unclear. This study aimed to determine the COVID-19 TPR dynamics of the Indonesian West Sumatra province in the rst year of documented cases. Methods: We conducted a retrospective study using secondary data of the COVID-19 quantitative reverse transcription-polymerase chain reaction (q-RT-PCR) test in West Sumatra Province from April 2020 to March 2021. To examine trends, we estimated TPR(s) on an annual, quarterly, and monthly basis in the province, its regions (cities/ regencies), and districts. Results: From a total of 410,424 individuals taking the COVID-19 q-RT-PCR examination during one year, the provincial TPR was 8.11%. The third quarter (October 2020 – December 2020, 12.18%) and October 2020 (15.62%) had the highest TPR quarterly and monthly, respectively. The TPR of cities was almost certainly twice that of regencies. Annual TPR varied signicantly (p<0.001) across regions, districts, and periods. Conclusion: The COVID-19 TPR trends in West Sumatra at the rst year of the pandemic were generally higher than the global recommendation. Further study on population density, public mobility, and implementation of health protocol in the province should be valuable to understand TPR dynamics.


Introduction
The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in humans, killed at least four million people in July 2021 (1,2). Indonesia reported 3.3 million cases and 92 thousand deaths at the same time. In West Sumatra Province, there were as many as 37 thousand cases, with 800 deaths (3). Meanwhile, the actual COVID-19 cases are considered higher than o cial records (4). Thus, some indicators in a large-scale community are required to estimate and control the pandemic.
The test positivity rate (TPR) is a reliable indicator for managing the COVID-19 pandemic (5). The World Health Organization (WHO) also uses COVID-19 TPR as a standard to determine the control level of SARS-CoV-2 transmission by dividing the number of positive con rmed cases by the number of people tested. A positivity rate of more than 5% in a particular area indicates that the outbreak has gone out of control and that a broader scope of mass screening is required(6). The q-RT-PCR test of SARS-CoV-2 genetic materials obtained from the nasopharyngeal or oropharyngeal swab is the COVID-19 standard diagnostic procedure. This examination is a benchmark of excellence for calculating the TPR to assess the level of outbreak control in a particular region (7,8) Although the COVID-19 TPR was considered essential in controlling the outbreak, the TPR analysis in the particular region of Indonesia remains unclear. To ll the gap, we evaluated all COVID-19 datasets in West Sumatra Province from April 2020 to March 2021. This study aimed to determine the COVID-19 TPR in the province at this period, including in its regions and districts. We also evaluate the TPR trends on a quarterly and monthly basis to discuss the control level of viral transmission in the areas. To our knowledge, this is the rst study describing COVID-19 TPR in a speci c province of Indonesia.

Study design and data collection
This research was an observational retrospective study. The study population consisted of people who took the COVID-19 q-RT-PCR test in West Sumatra Province between April 2020 and March 2021. The

De nition and statistical analysis
The COVID-19 test positivity rate (TPR) was de ned as the proportion of individuals who tested positive for COVID-19 for the rst time per all individuals who took the COVID-19 q-RT-PCR test at a given time. We de ned the specimen source as the district where the specimens were collected. We calculated the TPR(s) for the province, regions (cities and regencies), and districts based on periods (yearly, quarterly, and monthly). The chi-squared test or chi-squared for trends test was used to examine TPR differences between regions, districts, quarters, and months for a year. A p-value <0.05 was signi cantly different.

Characteristic of the test positivity rate
The TPR was 8.11% among 410,424 people who took the COVID-19 q-RT-PCR test in West Sumatra between April 2020 and March 2021 ( Table 1). The annual TPR of cities was nearly twice that of regencies. Kota Bukittinggi had the highest TPR (13.12%), followed by other major cities including Kota Padang Panjang, Kota Solok, and Kota Padang, which all have TPR above 10%. In the regency region, Agam had the highest TPR with 10.89%. Kota Sawahlunto (7.46%) and Dharmasraya (3.07%) had the lowest TPR in cities and regencies, respectively. TPR varied signi cantly across regions, districts, quarterly, and monthly. To provide TPR trends of West Sumatra province, we evaluated the one-year COVID-19 TPR quarterly and monthly by region (cities and regencies) (Figure 1). The provincial TPR increased signi cantly from 1.94% in the rst quarter to a high of 12.4% in the third quarter (Figure 2a). The TPR, on the other hand, has generally fallen in the last quarter. The trends in cities and regencies were similar, with cities having a TPR that was likely twice as high as regencies in each quarter. TPR in cities peaked at 15.8%, while TPR in regencies peaked at 8.3%.
The province's TPR trend decreased gradually during the rst three months of the annual period of study (Figure 2b). TPR reached its lowest point in June 2020, at 0.7%. However, there was a 15-fold increase in TPR from July 2020 to October 2020, with the highest peak point reaching 15.6%. Cities had a TPR of 22.05% at this point, nearly three times that of regencies, which had a TPR of 7.7%. Provincial TPR fell until January 2021, then rose again in February and March 2021, whereas city TPR rose earlier in January 2021. In general, the trend of TPR in the regencies was likely to follow that of the cities, except for December 2020, when the TPR in the regencies was slightly higher than that of the cities (8.08% versus 7.55%).
The highest TPR in West Sumatra was found in Kota Padang Panjang in the third quarter (23.73%), followed by Kota Solok in the fourth quarter ( Figure 3) (22.17%). The TPR(s) used to rise every quarter in six districts, namely Kota Bukittinggi, Kota Sawahlunto, Kota Solok, Kepulauan Mentawai, Lima Puluh Kota, and Solok Selatan. The TPR(s) also tended to rise monthly ( Figure 4 and Figure 5). The COVID-19 TPR trends in West Sumatra differed by region and district quarterly and monthly.

Discussion
As the SARS-CoV-2 transmission indicator, a large-scale COVID-19 TPR is frequently used to control the pandemic. The TPR could estimate COVID-19 prevalence, predict healthcare needs, and monitor the severity of cases in a country (11)(12)(13). To determine the COVID-19 TPR, we used retrospective q-RT-PCR results from April 2020 to March 2021 in West Sumatra Province. According to our ndings, the province's annual TPR exceeded the WHO recommendation of 5%. At its peak, the TPR exceeded 15%. The TPR of cities was approximately twice as high as regencies. The province's TPR trend increased signi cantly after the rst quarter, with a brief drop from December 2020 to January 2021.
A higher population density may induce a higher TPR. In the West Sumatra Province, the average population density of cities was likely 12 times higher than that of regencies (9,10). Based on this, we assumed that cities should represent the urban, while the regencies are rural (14). Our study showed that the cities had the higher TPR, consistent with the density. In the districts with a low population density (below 109 people per square kilometer in average) such as Dharmasraya, Kepulauan Mentawai, Pasaman, Solok Selatan, Padang Pariaman, and Pasaman Barat, the TPRs were observed lower. Also, some studies previously explained that population density is a determinant for SARS-CoV-2 transmission (15)(16)(17). However, we believed that other confounding factors should also in uence a high TPR in cities, such as higher mobility, so further study is needed.
Some studies highlighted the TPR as a more reliable indicator for predicting viral transmission than the incidence rates. The number of new cases depends on the capacity of the test, unlike the TPR. The larger the testing scale, the lower the TPR(18) , (19). However, in West Sumatra, the TPR was high (12.40%) when the COVID-19 testing capacity increased in the third quarter (140,210 tests). So, we predicted that the actual cumulative cases would be far higher than recorded and testing capacity merely insu cient, meaning the SARS-CoV-2 transmission was out of control. Moreover, in January 2021, the TPR fell to 5.79% after the cumulative test at its maximum quantity (61,415 tests) and surged again to 12.05% after testing capacity decreased about 60% in two months. Thus, massive testing is vital for nding the case and controlling outbreaks, especially when the transmission is high.
The TPR trends addressed people's mobility and behaviour in West Sumatra during a year. The TPR fell to the lowest point in June 2020 (0.75%) when the provincial government implemented a large-scale social distancing policy (PSBB) since April 2020. At this time, public facilities such as schools, o ces, houses of worship were closed, so social gatherings were prohibited(20). This nding was consistent with previous studies, which found that restricting public mobility was associated with a decrease in SARS-CoV-2 transmission (21)(22)(23). However, the rates sharply rose ten times in September 2020 as the government replaced PSBB with a new normal policy (TNBPAC) since the end of June 2020. This new regulation opened up public spaces under the implementation of health protocols such as hand washing, maskwearing, and physical distancing (24). Besides, misinformation about the COVID-19 policy resulting in ineffective health protocol implementation also contributed to the TPR surge (25,26). Therefore, government policies and public cooperation are vital in controlling pandemics. TPR trends at the regional level were similar to provincial. However, the TPR trends of the regencies were likely to follow the cities a month late, especially for the neighbouring districts. For example, the City of Kota Padang had a TPR peak of 22.66% in October 2020, while the neighbouring regencies of Solok and Padang Pariaman reached the peak a month later. This condition might be due to a higher viral transmission in cities and regencies-cities-regencies migration, though infection could have come from either region (27). Thus, controlling district borders may prevent viral spreading between regions.
This study is limited in the specimen source information that was only available from the location of the health facility sending the specimen, not from the individual's domicile origin. However, because the patient was present at the facility, it should also represent the virus in the district. Our study should contribute to a better understanding of TPR in estimating SARS-CoV-2 transmission in West Sumatra.

Conclusion
In summary, we here determine the COVID-19 q-RT-PCR TPR dynamics in West Sumatra. The TPR trends of the rst year of the pandemic were higher than the global recommendation, meaning that the SARS-CoV-2 transmission was uncontrolled. Possible factors that in uence the TPR level are population density, testing capacity, public mobility, and the implementation of health protocols. Further study should explore these factors to achieve a better approach to control the COVID-19 situation. This study assesses the COVID-19 prevention strategy in Indonesia, particularly in West Sumatra Province, and should provide valuable data for future COVID-19 control measurement.
writing review. AEP: supervision, conceptualization, data resources, methodology, writing review, validation. All authors have read and approved the manuscript.    COVID-19 test positivity rate trends of one-year period monthly in regencies.