A team of scientists from the Centers for Disease Control and Prevention, United States, recently conducted a study to evaluate the effectiveness of serial testing and isolation of healthcare personnel in nursing homes in preventing the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative pathogen of coronavirus disease 2019 (COVID-19). The findings reveal that frequent implementation of rapid testing in response to an outbreak is highly effective in reducing COVID-19 spread in nursing homes. The study is currently available on the medRxiv* preprint server.
The COVID-19 pandemic, which has already infected more than 75 million people globally, has placed a large burden on healthcare systems. In the United States, the majority of nursing homes have been severely affected by COVID-19. Several non-pharmacological control measures have been implemented to prevent the transmission of SARS-CoV-2 among residents and healthcare personnel in nursing homes. For example, serial testing strategies have been implemented to rapidly identify and isolate symptomatic people. However, to effectively contain the viral spread, it is important to identify asymptomatic and pre-symptomatic people as they are also likely to transmit the infection to others. According to recent guidelines of the Centers for Disease Control and Prevention (CDC), all residents and healthcare personnel in healthcare setups with or without outbreak should be tested at frequent intervals.
In the current study, the scientists conducted mathematical modeling analysis to estimate the effectiveness of “outbreak testing” with or without “non-outbreak testing” in identifying and isolating affected people, as well as to curb the SARS-CoV-2 transmission in nursing homes.
Current study design
The scientists defined “outbreak testing” as serial testing of all residents and healthcare personnel immediately after identification of a new COVID-19 case. In contrast, “non-outbreak testing” was denoted as serial testing of healthcare personnel in the absence of any new COVID-19 case.
The scientists used a Reed-Frost mathematical model to estimate the expected outbreak size at baseline. By considering that only symptomatic people were tested and isolated and recommended control measures were properly implemented, the scientists estimated the reproductive number (R0) for outbreaks, which were designated as “unmitigated” R0. The reproductive number (a mathematical term to indicate the infectivity of a pathogen) was used to estimate the outbreak size at baseline. In addition, they estimated the reduction in viral transmission expected from the outbreak testing approach.
They specifically evaluated how testing frequency (weekly, every-3-day, or daily), turnaround time (24-hour, 48-hour, or immediate), and testing sensitivity (95%, 85%, or 50%) may impact the transmission of SARS-CoV-2 in nursing homes.
The scientists estimated that weekly outbreak testing with 48-hour turnaround time and daily outbreak testing with 50% test sensitivity and immediate turnaround time (point-of-care testing) are capable of preventing 54% and 92% of COVID-19 cases, respectively. Moreover, they estimated that an additional 8% of cases could be prevented if outbreak testing is combined with weekly or every-3-day non-outbreak testing. The implementation of every-3-day outbreak and non-outbreak testing together with point-of-care testing was found to prevent 95% of COVID-19 cases.
Importantly, the scientists observed that increasing the testing frequency or reducing the turnaround time for outbreak testing is a better approach than combining outbreak and non-outbreak testing in reducing viral transmission.
With further analysis of this system, they observed a 10% reduction in infection control measures (isolation of infected people), a combination of outbreak and non-outbreak testing could prevent fewer cases than outbreak testing alone with full effectiveness of infection control measures. In other words, the extra benefits of non-outbreak testing are mostly nullified if the effectiveness of infection control measures is reduced simultaneously. Overall, the mathematical modeling analysis estimated that if accompanied by a reduction in the effectiveness of isolating infected people, outbreak testing alone is more effective than outbreak – non-outbreak combination in controlling the infection spread.
Evaluation of how the performance of testing strategies for nursing homes changes as the likelihood of a new SARS-CoV-2 introduction during the week of testing varies. The solid line depicts the percentage of cases prevented when combining outbreak and non-outbreak testing. The dotted line shows tests per case prevented when combining outbreak and non-outbreak testing. Both lines show results for outbreak and non-outbreak testing conducted every 3 days with immediate turnaround (i.e., point-ofcare test) and 85% test sensitivity (compared to a reverse-transcriptase polymerase chain reaction [RT-PCR] test).
Overall, the study findings indicate that testing of asymptomatic people during an outbreak is an effective approach to supplement recommended control measures and control infection spread in nursing homes. The effectiveness of outbreak testing can be improved by increasing the testing frequency, reducing the turnaround time, and properly implementing the infection control measures.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.