COVID-19 is diagnosed by the detection of the SARS-CoV-2 virus by a real-time reverse transcriptase PCR (RT-PCR) assay using nasopharyngeal and oropharyngeal (NP/OP) samples. However, a negative test result does not necessarily rule out the disease in an individual.

Winichakoon and associates at Chiang Mai University, Thailand reported a case of a 28-year-old male who presented with complaint of high fever and malaise for 3 days. He also had rhinorrhea and cough, which had resolved.

There was a travel history from Jinzhou, China, to Chiang Mai with a transit in Wuhan, China. He was admitted to an airborne infection isolation room, and NP/OP swabs were taken for testing. The RT-PCR assay results came out as negative for SARS-CoV-2.

The patient underwent chest X-ray examination on day 3 of hospitalization, which did not show any infiltration. Fever persisted without any other respiratory symptoms. On day 5, the NP/OP swab results again came out to be negative. On day 7, the patient developed nonproductive cough. Chest X-ray showed bilateral lower lung infiltrates with prominence on the right side, consistent with viral pneumonia. 

On day 8 bronchoalveolar lavage (BAL) fluid tested positive for the virus. On day 10, the patient’s condition improved, his appetite increased, and fever resolved. He was discharged on day 18.

Message - A negative NP/OP swab result does not rule out COVID-19, particularly when the history raises the suspicion of the disease. 

Source: Winichakoon P, Chaiwarith R, Liwsrisakun C, et al. Negative Nasopharyngeal and Oropharyngeal Swabs Do Not Rule Out COVID-19. J Clin Microbiol. 2020 May; 58(5): e00297-20.