The 2019-nCoV is a bete-coronavirus in the same subgenus as the Severe Acute Respiratory Syndrome (SARS), but is quite different from the Middle East Respiratory Syndrome coronavirus (MERS-CoV) . Due to the high human-to-human transmission rate, COVID–2019 spreads worldwide rapidly. Considering the grim situation, the World Health Organization (WHO) declared the global outbreak of 2019-nCoV constitutes a public health emergency of international concern (PHEIC) on January 31, 2020.
Currently, the incubation period for COVID–19 pneumonia is thought to be within 14 days following exposure, with most cases at approximately 3–7 days after exposure. The most important criteria for diagnoses of COVID–2019 pneumonia is positive RT-PCR results, which could be performed on the blood, body fluids, nasopharyngeal and oropharyngeal swab，sputum，bronchoalveolar lavage and stool specimens. It has been reported that only when there are negative results of RT-PCR testing for 2019-nCoV on two specimens collected ≥24 hours apart, a patient can release from quarantine. However, the accuracy of RT-PCR test of any virus would not be 100%. In other words, false negative would be inevitable in some clinical cases. The accuracy is related to the severity and stage of the patients’ disease. According to the current,patients with clinical manifestations and pneumonia confirmed imaging tests can be clinically diagnosed as COVID–2019 pneumonia in Hubei Province. Therefore, we still highly suspect this patient has COVID–2019 pneumonia regardless of his multiple negative RT-PCR test results. When the patients are in the early or recovery stage of the disease, the detection rate of 2019-nCoV tests are also probably lower. Sometimes, laboratory errors, wrong specimen type or virus detection kit can also be the cause of false negative test results. The most preferred specimens is nasopharyngeal swab, followed by oropharyngeal swab, then sputum. Now it is also possible to improve the positive rate by collecting nasopharyngeal swab and oropharyngeal swab in the same specimen collection tube.
In summary, when patients show the characteristic clinical manifestations of COVID–2019 pneumonia and chest CT typical for COVID–2019 pneumonia, and has recent history of exposure to people came back from Hubei Province, COVID–2019 should be highly suspected and appropriate treatment and isolation are still needed, even when the RT-PCR results repeatedly to be negative up to five times.