Epidemiology of COVID-19 and effect of public health interventions, Chennai, India, March - October 2020

Objectives

To describe the public health strategies and their effect in controlling the COVID-19 pandemic from March to October 2020 in Chennai, India.

Setting

Chennai, a densely populated metropolitan city in Southern India, was one of the five cities which contributed to more than half of the COVID-19 cases in India.

Participants

We collected the de-identified line list of all the 192,450 COVID-19 case-patients reported from 17 March to 31 October 2020 in Chennai and their contacts for the analysis. We defined a COVID-19 case-patient based on the RT-PCR positive test in one of the Government approved labs.

Outcome measures

The primary outcomes of interest were incidence of COVID-19 per million population, case fatality ratio, deaths per million and the effective reproduction number (R _t ). We also analysed the indicators for surveillance, testing, contact tracing and isolation.

Results

Of the 192,450 RT-PCR confirmed COVID-19 case-patients reported in Chennai from 17 March-31 October 2020, 114,889 (60%) were males. The highest incidence was 41,064 per million population among the 61-80 years. The incidence peaked during June 2020 at 5239 per million and declined to 3,627 per million in October 2020. The city reported 3,543 deaths, with a case fatality ratio (CFR) of 1.8% and the crude death rate was 431 per million. When lockdown began, Rt was high (4.2) in March and fluctuated from April to June 2020. The R _t dropped below one by the first week of July and remained so until October 2020, even with the relaxation of restrictions

Conclusion

The combination of public health strategies controlled the COVID-19 epidemic in a large, densely populated city in India. We recommend continuing the interventions to prevent resurgence, even as vaccination is being rolled out.

Strengths

• We did a comprehensive analysis of COVID-19 strategies and outcome in a large, densely populated metropolitan city in India.

• We documented that the community-centric public health strategies were feasible and effective in controlling the COVID-19 outbreak even in a large, thickly populated city

• The lessons learnt are relevant to similar settings in low-and middle-income countries. Given the ongoing multiple waves of COVID-19 and the difficulty in controlling the transmission, our experience and lessons learnt will be valuable for policymakers and scientific advisors globally

Limitations

• We analysed the data available from the GCC database and not from the hospitals where patients with moderate to severe illness were admitted. Hence, we could not report the severity of illness among admitted patients.

• Second, the COVID-19 incidence might have been underestimated while testing was low during the early phase of the epidemic