Mass testing in big cities like Lusaka may limit COVID-19 spread, but is it practical?

In 2020, computer models predicted that COVID-19 spread in large cities could be better controlled by mass testing, and by then isolating all those who tested positive. However, researchers said this approach may be costly and impractical.

Early in the pandemic, many people that were infected with COVID-19 showed no signs of the disease and still spread the disease to others. Some studies suggested that 50% to 80% of people with COVID-19 didn’t have symptoms (asymptomatic) and may have been responsible for 40% to 70% of new infections.

Researchers wanted to know if finding and isolating asymptomatic people would help to control COVID-19 spread. They also wanted to know if banket-testing, which means testing many people randomly, effectively finds asymptomatic people.

The researchers created a computer model that predicts how people go from being susceptible to exposed, infected, and isolated. They focused on data from the Lusaka province in Zambia, which is a corporate hub with an international airport that borders two countries.

Because the characteristics of COVID-19 seemed to vary from place to place, they looked at 4 scenarios, where either 50% or 70% of COVID-19 cases were asymptomatic, and these cases were either equally or half as infectious as symptomatic ones.

The researchers’ model found that it was possible to control the spread of COVID-19 by performing blanket tests and by isolating all people who tested positive, even those without symptoms. They said that to have reduced the peak number of cases by 90% across all scenarios, 10% of the people in Lusaka needed to be tested every day. They also found that if we wanted to keep the number of new COVID-19 infections constant, 22% of people needed to be tested every day.

Despite Zambia putting many COVID-19 limiting measures in place, the cases still seemed to rise. Blanket testing effectively reduced the number of COVID-19 cases by 90% in a small town in Italy. But, there are no previous studies to suggest it would be effective in a large city elsewhere.

Note that the researchers did not actually do blanket testing in this study; rather they created a model that suggests blanket testing would work to limit COVID-19 spread in larger cities. However, they warned that it would likely be too expensive. They also said it might be more practical when combined with other measures, such as lockdowns, contact tracing, and vaccination.

The Zambian researchers also stressed that asymptomatic COVID-19 cases seemed to be more common in Africa at the time. 

Abstract

Introduction

The novel Coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus—2 (SARS-CoV-2), in Africa is characterised by a more substantial proportion of asymptomatic (or mildly symptomatic) individuals thought to be playing a role in the spread of the infection. The exact proportion and degree of infectiousness of asymptomatic individuals remains unclear. Studies however indicate that their management is crucial for control of SARS-CoV-2 transmission.

Methodology

We developed a simplified deterministic susceptible-exposed-infectious-removed (SEIR) mathematical model to assess the effect of active isolation of SARS-CoV-2 infected but asymptomatic individuals through blanket testing for control of the outbreak in Lusaka Province of Zambia. Here we modelled two scenarios; (1) assuming asymptomatic individuals comprised 70% of all COVID-19 cases and (2) asymptomatic individuals comprised only 50% of the cases. For contrast, the model was assessed first under the assumption that asymptomatic individuals are equally as infectious as symptomatic individuals and then secondly, and more likely, assuming asymptomatic individuals are only half as infectious as symptomatic individuals.

Results

For the model assuming 70% asymptomatic cases, a minimum sustained daily blanket testing rate of ≥ 7911 tests/100000 population was sufficient to control the outbreak if asymptomatic individuals are only half as infectious while if equal infectiousness was assumed then a testing rate of ≥ 10028 tests/ 100000 population would be required. For 50% asymptomatic, minimum blanket testing rates of ≥ 4540 tests/ 100000 population was sufficient to control the outbreak at both assumed levels of infectiousness for asymptomatic individuals relative to symptomatic individuals.

Discussion and conclusion

Our model predicts that active isolation of COVID-19 cases, including asymptomatic individuals, through blanket testing can be used as a possible measure for the control of the SARS-Cov-2 transmission in Lusaka, Zambia, but it would come at a high cost.

Disclaimer

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