More data are needed to make data-driven policy decisions on the effectiveness of individual quarantine vs active monitoring of contacts to reduce the spread of coronavirus disease 2019 (COVID-19), according to study results recently published in The Lancet Infectious Diseases.
In December 2019, an outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged from Wuhan, China, and has spread globally, from >3.5 million confirmed cases of COVID-19 as of May 2020, when study results were first published online in The Lancet, to >29.6 million in September 2020. Governments have implemented community measures to reduce further spread of the disease, including increasing physical distance, travel restrictions, and temperature checks. Currently, there are 2 essential nonpharmaceutical approaches to help prevent disease spread: voluntary individual quarantine and voluntary active monitoring.
Individual quarantine involves a person who may have been exposed to the disease but is not showing symptoms to separate themselves from others. The less-restrictive approach of active monitoring involves assessing the person who may have been exposed to the disease for symptoms at regular intervals (eg, twice-daily visits by healthcare workers or phone-based self-monitoring) and to trace the other individuals with whom this person has come in contact. The amount of disease transmission that occurs before symptom onset greatly affects the effectiveness of these 2 approaches and the ability to control outbreaks. Therefore, this study compared the effectiveness of individual quarantine and active monitoring targeted by contract tracing.
A stochastic branching model was fit to reported parameters for the dynamics of the disease to compare the efficacy of individual quarantine and active monitoring of contacts to control the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The model was tailored to the incubation period distribution (mean, 5.2 days) and to 2 estimates of the serial interval distribution: a shorter one (mean serial interval, 4.8 days) and a longer one (mean serial interval, 7.5 days).
Investigators derived the incubation period of 5.2 days from a previous study in 451 laboratory-confirmed cases in Wuhan, China, and assessed variable resource settings using 2 feasibility models: a high-feasibility setting and a low-feasibility setting. The high-feasibility setting assumed 90% of contacts traced with a half-day delay in tracing and symptom recognition and 90% effective isolation. The low-feasibility setting assumed 50% of contacts traced with a 2-day average delay in tracing and symptom recognition and 50% effective isolation.
Results showed the effectiveness of the 2 approaches is dependent on the assumptions regarding the serial interval, the amount of presymptomatic transmission that occurs, and the feasibility setting. Model fitting by sequential Monte Carlo resulted in a mean time of infectiousness onset before symptom onset to be 0.77 days for the shorter serial interval and 0.51 days for the longer serial interval.
Under the fitted disease natural history parameters for serial interval scenario 1 (mean of 4.8 days and high amount of presymptomatic transmission), individual quarantine was considerably more effective than active monitoring. In high-feasibility settings where ≥75% of infected contacts are quarantined, individual quarantine contained the outbreak with a short serial interval 84% of the time; however, in low-feasibility settings where the outbreak continues to grow, the burden of the number of contacts traced for active monitoring or quarantine will grow, too.
Under the fitted disease natural history parameters for serial interval scenario 2 (mean of 7.5 days and low amount of presymptomatic transmission), both active monitoring and individual quarantine effectively reduced the expected number of secondary cases per contact to <1. Individual quarantine showed no real benefit compared with active monitoring; however, if individual quarantine leads to a decrease in the percentage of contacts traced because of hesitation or avoidance, active monitoring may become more effective.
Overall, the study authors concluded, “The conflicting conclusions from our two scenarios, driven largely by the differences in the extent of presymptomatic transmission, highlight the urgent need for more data to clarify key epidemiological parameters of COVID-19, particularly the serial interval and the extent of presymptomatic transmission, to inform response efforts.”
Peak CM, Kahn R, Grad YH, et al. Individual quarantine versus active monitoring of contacts for the mitigation of COVID-19: a modelling study. Lancet Infect Dis. 2020;20:1025-1033.