Small Chinese study examines characteristics of asymptomatic infection with SARS-CoV-2
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Asymptomatic infection with SARS-CoV-2, the virus that causes COVID-19, occurred most often among adults aged 30 to 49 years, according to results from a single-center study in Shenzhen, China, that was published in The Journal of Infectious Diseases.
“Results indicated that the screened asymptomatic cases were just the tip of the iceberg of the COVID-19 [outbreak]. The majority of asymptomatic cases infected with SARS-Cov-2 wandered outside the isolation ward,” Yanrong Wang, MD, of the National Clinical Research Center for Infectious Disease and Shenzhen Third People’s Hospital, told Healio. “Those asymptomatic cases are the important source of infection. Dealing with the problem is critical to stopping the virus from spreading further.”
Wang and colleagues identified 55 asymptomatic instances of SARS-CoV-2 infection among patients admitted to the Third People’s Hospital of Shenzhen from Jan. 11, 2020 to Feb. 29, 2020. Patients were admitted following a family member’s COVID-19 diagnosis. Patients with suspected cases of COVID-19 who had symptoms, including fever, cough, fatigue, poor appetite, headache and diarrhea, at the time of admission were excluded from the study. Clinical outcomes were examined for each patient.
The 55 cases included 22 men and 33 women aged 2 to 69 years, with a median age of 49 years. A total of 30.9% of the cases occurred in patients aged 30 to 49 years and more than half of the patients were native to Hubei Province. Additionally, 70.9% of the asymptomatic cases eventually transformed into a typical case of COVID-19.
Only seven of the 55 patients experienced a mild cough; seven cases had a low fever 3 to 5 days later. All cases were put into medical isolation on admission, despite being asymptomatic. The time from hospitalization to onset of illness was 1 to 7 days.
CT scans were normal in 16 (29.1%) of the cases; no symptoms occurred in this group. Pneumonia was found on CT scans in 37 patients at the time of admission.
While the findings presented in the study were novel, Wang did note that the definition of an asymptomatic case needed to be clarified further. In addition, not all chest CTs were examined on day one of hospital admission because of the radiology department’s schedule.
“Many middle-aged women in China would rather not speak out about their sickness,” Wang said. “There is a bias that asymptomatic cases were judged according to the chief complaint in the medical record.”
The researchers were also surprised that CT showed pneumonia in 37 of 55 cases on admission.
“The infection is estimated to have a mean incubation period of 5.2 days,” Wang said. “It could be that chest imaging showed abnormalities prior to clinical presentations.” – by Eamon Dreisbach
Disclosure: Wang reports no relevant financial disclosures.
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