Chlamydia psittaci infection in humans, also known as psittacosis, is usually believed to be an uncommon disease which mainly presents as community-acquired pneumonia (CAP). It is usually sporadic, but outbreaks of infection may occasionally occur. In outbreaks, diagnosis and investigations were usually hampered by the non-specificity of laboratory testing methods to identify C. psittaci. In this study, we use metagenomic next-generation sequencing (mNGS) in the diagnosis of a family outbreak of psittacosis under COVID-19. Three members of an extended family of 6 persons developed psittacosis with pneumonia and hepatic involvement with common symptoms of fever and weakness. Two newly purchased pet parrots which had died successively were probably the primary source of infection. Imagings show lung consolidations and infiltrates, which are difficult to be differentiated from CAP caused by other common pathogens. mNGS identified the infecting agent as C. psittaci rapidly within 48h. The results of this work suggest that there are not characteristic clinical manifestations and imagings of psittacosis pneumonia which can differentiate from CAP caused by other pathogens.The use of mNGS can improve accuracy and reduce the delay in diagnosis of psittacosis especially during the outbreak, which can shorten the course of the disease control. Family outbreak under COVID-19 may be related to the familial aggregation due to the epidemic. To our knowledge, this is the first reported family outbreak of psittacosis in China, and the first reported psittacosis outbreak identified by the method of mNGS in the world.

Psittacosis pneumonia is easily underdiagnosed and misdiagnosed. In this study, we use mNGS in the diagnosis of psittacosis pneumonia.