Pandemic Tied to Misdiagnosis of Rare Pneumonia

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Psittacosis, a rare disease, has been underdiagnosed or misdiagnosed during the COVID-19 pandemic, likely because the symptoms of the disease are similar to COVID-19 symptoms, researchers suggest on the basis of data from 32 individuals.

Diagnosis of and screening for COVID-19 continues to increase; however, cases of atypical pneumonia caused by uncommon pathogens, which presents with similar symptoms, may be missed, wrote Qiaoqiao Yin, MS, of Zhejiang Provincial People’s Hospital, China, and colleagues.

“The clinical manifestations of human psittacosis can present as rapidly progressing severe pneumonia, acute respiratory distress syndrome, sepsis, and multiple organ failure,” but human cases have not been well studied, they say.

In a study published in the International Journal of Infectious Diseases, the researchers reviewed data from 32 adults diagnosed with Chlamydia psittaci pneumonia during the COVID-19 pandemic between April 2020 and June 2021 in China. The median age of the patients was 63 years, 20 were men, and 20 had underlying diseases.

A total of 17 patients presented with fever, cough, and expectoration of yellow-white sputum. At the time of hospital admission, three patients had myalgia, two had headache, and two had hypertension. The patients were originally suspected of having COVID-19.

“All patients showed atypical pneumonia, including inflammatory infiltration, pleural effusion, multiple inflammatory exudative lesions with interstitial edema, lung abscesses and white lung,” all of which could be observed in COVID-19 patients as well, the researchers write.

RT-PCR and ELISA testing were used to rule out COVID-19. The researchers then used metagenomic next-generation sequencing (mNGS) to identify the disease-causing pathogens. They collected 18 bronchoalveolar lavage fluid (BALF) samples, nine peripheral blood samples, and five sputum samples. The mNGS identified C psittaci as the suspected pathogen within 48 hours. Suspected C psittaci infections were confirmed by endpoint PCR for the BALF and sputum samples and 6 of 9 blood samples, “indicating a lower sensitivity of PCR compared to mNGS for blood samples,” the researchers say. No other potential pathogens were identified.

Psittacosis is common in birds but is rare in humans. C psittaci is responsible for 1% to 8% of cases involving community-acquired pneumonia in China, the researchers note. Although poultry is a source of infection, 25 of the patients in the study did not report a history of exposure to poultry or pigeons at the time of their initial hospital admission. Many patients may be unaware of exposures to poultry, which further complicates the C psittaci diagnosis, they note.

All patients were treated with doxycycline-based regimens and showed improvement.

The findings were limited by several factors, including the lack of a definitive diagnostic tool for C psittaci and the lack of convalescent serum samples to confirm cases, the researchers note. In addition, molecular detections for PCR are unavailable in most hospitals in China, they say. The results represent the largest known collection of suspected C psittaci pneumonia cases and highlight the need for clinician vigilance and awareness of this rare condition, especially in light of the potential for misdiagnosis during the ongoing COVID-19 pandemic, they conclude.

The study received no outside funding. The researchers have disclosed no relevant financial relationships.

J Infect Dis. Published online July 12, 2022. Full text

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