Why do residents who are negative have to be tested repeatedly？

Why are residents who tested negative for nucleic acid required to undergo repeated nucleic acid testing? There are three reasons.

Firstly, in terms of clinical disease occurrence and development, any pathogenic infection has a certain incubation period, and the COVID-19 is no exception, and there are some individual differences in the length of the incubation period. The incubation period is the time between the invasion of the pathogen into the body and the earliest appearance of clinical symptoms. Repeated nucleic acid testing can be used to detect cases early in the incubation period before clinical symptoms appear.

Secondly, in terms of detection technology, there is the concept of a detection period. The virus has a growth and replication process in the body after infection, and the viral load at the beginning of the infection is so low that a positive test cannot be detected, and this is the detection period. Repeated testing can increase the chances of detecting a positive test and detecting a positive test in time.

Thirdly, sampling for respiratory pathogens is mainly done in the form of pharyngeal swabs, nasal swabs and nasal + pharyngeal swabs, and there is inevitably some sampling variation in the sampling process, which includes the sampling site, depth and the number of secretions collected. Repeated sampling tests can compensate for the possible false negative effects of sampling errors.

In general, repeat testing allows for early detection of cases, especially asymptomatic infections, identification and targeting of risk areas and key populations for timely and targeted control measures to halt the spread of the epidemic.