![]() ![]() The sensitivity of PCR tests at any given point during infection depends upon the amount of viral RNA present this increases at the start of the infection up to the peak viral load, which appears to occur just before, or at, the time of symptom onset. ![]() ![]() In the UK, testing commonly uses polymerase chain reaction (PCR) to detect the presence of viral ribonucleic acid (RNA) in the nasopharynx of those sampled. ![]() Both of these populations have a substantially higher risk of fatality from COVID-19 infection than the general population. Alternatively, healthcare workers (HCWs) may be routinely tested to prevent nosocomial transmission to patients who may have other comorbidities. For instance, residents and staff in care homes may be tested regularly to minimise outbreaks among elderly populations. Our results suggest that routine asymptomatic testing can enable detection of a high proportion of infected individuals early in their infection, provided that the testing is frequent and the time from testing to notification of results is sufficiently fast.ĭetection of current infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a crucial component of targeted policy responses to the COVID-19 pandemic that involve minimising infection within vulnerable groups. We estimated that testing every other day would detect 57% (33–76%) of symptomatic cases prior to onset and 94% (75–99%) of asymptomatic cases within 7 days if test results were returned within a day. Our results suggest a substantially higher probability of detecting infections 1–3 days after infection than previously published estimates. We estimated that the probability that the PCR test detected infection peaked at 77% (54–88%) 4 days after infection, decreasing to 50% (38–65%) by 10 days after infection. We jointly estimated times of infection and the probability of a positive PCR test over time following infection we then compared asymptomatic testing strategies by calculating the probability that a symptomatic infection is detected before symptom onset and the probability that an asymptomatic infection is detected within 7 days of infection. We fitted a Bayesian statistical model to a dataset of twice weekly PCR tests of UK healthcare workers performed by self-administered nasopharyngeal swab, regardless of symptoms. The effectiveness of routine asymptomatic testing will therefore depend on testing frequency and how PCR detection varies over time. Although the peak sensitivity of RT-PCR can be high, the probability of detecting an infection will vary throughout the course of an infection. Routine asymptomatic testing using RT-PCR of people who interact with vulnerable populations, such as medical staff in hospitals or care workers in care homes, has been employed to help prevent outbreaks among vulnerable populations. ![]()
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