dcyphr | False negative rate of COVID-19 is eliminated by using nasal swab test


*Letter to the editor*

There are many studies on the COVID-19 outbreak. Lan et. al reported a positive test on discharged patients. The author is reporting data on discharged patients who tested positive for the disease in Guangzhou City, China. 

The data is from the "Guangzhou Center for Disease Control and Prevention". The data included when the patient had symptoms, diagnosis date, discharge date, date when they tested positive. Discharged patients had the following criteria: a) normal temperature after 3 days, b) no symptoms, c) better results on CT scans, d) 2 negative "nucleic acid tests" taken 1 day apart.

161 discharged patients were re-tested. 22 patients were positive for the disease. The time between discharge and positive re-test shows that doctors discharged them too soon. The current 14-day observation needs to be extended. 

Before discharge, hospitals tested patients by throat and anal swabs. After discharge, doctors used nasal swabs which led to more positive cases. The 22 positive retests means that institutions should increase discharge standards. The authors tested 3 discharged patients with nasal swabs. All 3 patients retested positive.

The authors note that there were two family clusters retested.

Zou LR et al. noticed there were more viral loads in the nose than the throat. We should use nasal swabs to reduced false-negatives. One patient gave multiple types of samples but only 1 tested positive. The authors suggest testing different parts of the body for COVID-19.

There were 8 patients testing positive only on the fourth test. This means there is a high rate of false-negatives. We do not know the duration of the disease. Our current knowledge on its characteristics are insufficient. We need to collect more information.