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(11–13). 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 findings, 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 significantly after the first 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(15–17). However, we believed that other confounding factors should also influence 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 insufficient, 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 finding 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, offices, houses of worship were closed, so social gatherings were prohibited(20). This finding was consistent with previous studies, which found that restricting public mobility was associated with a decrease in SARS-CoV-2 transmission(21–23). 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, mask-wearing, 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.