Monitoring the Spread of SARS-CoV-2 Is an Important Public Health Task

The unique characteristics of  severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have made the virus difficult to control. Asymptomatic or presymptomatic individuals account for a substantial portion of SARS-CoV-2 transmission. The high reproductive number (R₀) of SARS-CoV-2 creates the risk of exponential growth in localities where the virus has not been completely eradicated. The natural immunity period is relatively short (6–24 months). Furthermore, noncompliance with measures to control SARS-CoV-2 spread can lead to devastating public health consequences.¹ Considering the currently observed level of noncompliance with public health policies, the desirable goal of SARS-CoV-2 eradication looks elusive. As an endemic disease, COVID-19 will remain a threat. As the virus mutates, it will likely circulate throughout the globe in waves, requiring regular revaccinations. Therefore, effective public health policy² requires a robust public health surveillance system.

In this issue of AJPH, Hallal et al. (p. 1542) beautifully demonstrate the importance of sequential serological surveys to study the local spread of the virus. In the Brazilian State of Rio Grande do Sul, eight serological surveys of antibodies against SARS-CoV-2 were assessed over six months using a rapid point-of-care test performed on blood drops from a pinprick (sensitivity = ∼85%; specificity = 99.9%). Notably, the authors observed a time-dependent decline in sensitivity (up to only 42%) and applied appropriate statistical modeling to correct the decline in sensitivity over time. The study documented the spread of the pandemic in the Rio Grande do Sul, illustrating differences between Brazilian regions and suggesting the importance of local policies. Such surveys are extremely important for the timely development and implementation of local public health policies. The study by Hallal et al. is an excellent example of the statewide survey, facilitating collaboration between scientists and policymakers, public health experts, and politicians.

Many additional factors can contribute to the prolonged course of the pandemic, raising questions about the best approaches to monitor the spread of the virus. SARS-CoV-2 can be transmitted between humans and cats living in the same household, and there is evidence of cat to cat transmission.³ Similarly, transmission between humans and other domestic and wild animals cannot be completely ruled out. The role of environmental reservoirs in the transmission and spread of SARS-CoV-2 is not clear.

As SARS-CoV-2 replicates in the gastrointestinal tract, sewage testing was recently recognized as an adjunct to patient-based surveillance and a valuable tool to assess the spread of the virus.⁴ Furthermore, wastewater can be used to study the epidemiology and diversity of SARS-CoV-2 variants circulating in a community and identify new outbreaks.⁵ Comparison of various surveillance methods is needed to develop the best approach. It is possible that a combination of different surveillance approaches might be needed for timely assessment of viral spread and early detection of outbreaks.

The COVID-19 pandemic has highlighted the notion of health care as a constellation of sociotechnical systems that integrate people, technology, infrastructure, culture, goals, and processes. In the modern world, a strong public health system is the foundation and innovation-driving force. A successful example of serological surveys to study the local spread of the virus in a community is a first step on the path to effective public policy and the public health messaging necessary to suppress the spread of SARS-CoV-2.