In a recent study published in medRxiv* Preprint server Researchers have developed a model to reconstruct estimates of the number of travelers who would have tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the country of departure. They used data from French Polynesia, where they conducted SARS-CoV-2 screening upon arrival at the airport in a systematic manner.
background
Passengers arriving at the airport have been screened and tested for Coronavirus disease 2019 (COVID-19) in several countries. Individuals infected with COVID-19 were then isolated to control the spread of the disease. Although some countries reported the number of infected individuals detected upon arrival over time, this data was primarily limited to small testing programs that lasted for a short time. Thus, there is a lack of systematically reported long-term SARS-CoV-2 test data for travelers arriving at an airport on a global scale.
Despite the inconsistency in the reporting of COVID-19 testing data at the airport, it provides a unique opportunity to monitor SARS-CoV-2 in many countries. However, the challenge is that infections detected among incoming travelers reflect only a subset of all individuals infected with SARS-CoV-2.
about studying
In this study, researchers used data from more than 220,000 COVID-19 tests conducted on travelers who arrived in French Polynesia between July 2020 and March 2022 to estimate the prevalence of SARS-CoV-2 at airport departures in several countries.
French Polynesia has experienced three pandemic waves of COVID-19 caused by wild-type, delta, and omicron SARS-CoV-2 variants. Among incoming travelers, 15% of the measured cycle threshold values were less than 20, with a lower distribution in health care worker self-testing. Most travelers who entered French Polynesia had their journey origin either from the United States or metropolitan France.
During the first monitoring phase, travelers adhered to the COV-CHECK self-test protocol that was performed four days after arrival. In addition, travelers performed a reverse transcriptase-polymerase chain reaction (RT-PCR) test within 72 hours of departure. Later in February 2021, quarantine also became mandatory in this protocol.
The researchers also evaluated whether the access screening can reliably estimate the dynamics of international SARS-CoV-2. To this end, they converted SARS-CoV-2 prevalence upon departure, reflecting current positivity into an estimate of new daily infections. Furthermore, they compared the cumulative SARS-CoV-2 infection rate during this time as repeated serosurveys in France and the USA.
Results
There were 1,341 positive access tests in the study data set, with significant differences in weekly prevalence throughout the epidemic. The researchers noted that the growth and deterioration of the epidemic affected the detection of COVID-19 cases. For example, they estimated a 60% detection rate for SARS-CoV-2-infected individuals by RT-PCR assay of arrival on day 4 of arrival, during the first 10 days of infection, when the epidemic at the site of departure was increasing. At a rate of 10% per day. This rate would have been reduced to 40% during the pandemic which would have been dropping by 10% per day.
Interestingly, the spread of SARS-CoV-2 measured upon arrival of travelers from the United States or France predicted the actual COVID-19 dynamics in the two countries. Indeed, traveler testing served as a leading indicator and showed that peaks in the prevalence of SARS-CoV-2 occurred shortly before the peak in reported cases. It is also responsible for delays in the onset of COVID-19 symptoms and testing and reporting of case(s) in the country of origin.
Adapting to passenger testing protocols, the study model estimated the peak infection prevalence at departure in France and the United States in late 2020/early 2021 at 2.8% and 1.1%, respectively. Omicron BA.1 wave caused a prevalence of SARS-CoV-2 of 5.4% and 5.5% in France and the United States in early 2022, respectively. In France, the estimate of the cumulative incidence of COVID-19 in late 2020 was slightly greater than what was shown by serological studies. There are multiple explanations for the observed discrepancies. First, travelers from France declined during that period, which could affect the representation of travelers.
While risk-averse individuals were less likely to travel, risk-takers should be more likely to contract COVID-19 while in transit. Then, there is a possibility that some travelers may have contracted SARS-CoV-2 infection after their arrival. In French Polynesia, they conducted a SARS-CoV-2 test in travelers four days after their arrival. By contrast, the study estimates for the USA were consistent with increases in seroprevalence during the COVID-19 pandemic in late 2020 and 2021.
Conclusions
The study’s analysis highlighted the usefulness of routine traveler testing at airports. The results of the study provided a proof of concept for ongoing management of COVID-19 and future planning for the pandemic. He stressed the importance of systematic collection of test data with minimal correlation to enable real-time estimation of the underlying COVID-19 pandemic dynamics in many countries. These ideas will remain the same internationally or major global travel hubs. Furthermore, these endeavors will allow the synthesis of SARS-CoV-2 prevalence estimation across datasets, narrowing the uncertainty and significantly expanding the network of countries included.
*Important note
medRxiv publishes preliminary scientific reports that are not subject to peer review, and therefore should not be considered conclusive, guide clinical practice/health-related behavior, or be treated as established information.
Originally published at San Jose News Bulletin
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