Use of Proxy Indicators to Interpret the Epi Curve of COVID-19 in Sri Lanka

Sri Lanka has taken measures to avoid the introduction and spread of COVID-19 well before the country confirmed its first COVID 19 case on 27th January 2020, on top of its detailed epidemiological surveillance and infectious disease control system. Traditional indicators such as the daily case numbers have been used as an indicator to keep track of the outbreak progression. However, as the pandemic continued, the need to have proxy indicators was felt, both to better understand its behavior as well as future trends. The objective of this study was to explore the use of proxy indicators, namely the observed test positivity rate (TPR) and the mobility trends against the epidemic curve to interpret the behavior of the COVID-19 pandemic; their usefulness, and limitations. The information for the study was gathered using the COVID-19 daily status reports published and made publicly available by the Sri Lankan health authorities for the duration of 01/04/2021 to 30/06/2021. Trends of change of mobility during the period are gathered using regularly updated Google Community Mobility Reports. It is seen that the ‘trend’ of cases as depicted by weekly Observed TPR carries better information for decision making and evaluation of the methods to contain COVID 19 than using traditional proxy indicators such as the daily case numbers. The reported numbers in cases can be less than the actual numbers due to non-detection of cases in the community, under-reporting, delays in reporting, and PCR backlog. Trends of mobility changes and the trends of observed TPR together can be used to monitor and evaluate the effectiveness of the use of lockdown measures to contain the disease. It is recommended to adopt the use of such proxy indicators both in measuring the disease severity and the evaluation of the use of travel restrictions to contain the disease cost-effectively in a resource-limited setting.