COVID-19 in asymptomatic patients mild but still highly infectious

Asymptomatic carriage of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is more likely among middle-aged adults, according to a new Shenzhen, China study. In these cases, the disease turned out to be mostly mild in severity.

“The risk of virus spread within asymptomatic infection patients suggests that it is important to timely supervise the family members of coronavirus disease 2019 (COVID-19),” investigators said.

After a review of medical records, the investigators identified 55 asymptomatic SARS-CoV-2 patients (median age, 49 years; 33 females), testing positive for viral RNA. Almost a third (30.9 percent) were between 30–49 years of age and 70.9 percent eventually developed typical COVID-19 symptoms. [J Infect Dis 2020;doi:10.1093/infdis/jiaa119]

Despite being asymptomatic, patients were hospitalized and isolated as soon as they were identified as carriers. Illness developed 1–7 days after admission. Seven participants had coughs and seven reported a low fever 3–5 days later; two patients presented with both. Chest computed tomography (CT) was performed on all patients upon admission.

CT found pneumonia in 37 patients. In the remaining 16, initial chest imaging returned with normal results, and these patients did not develop symptoms over the course of hospitalization.

All patients received a combination of lopinavir and ritonavir, with treatment lasting for 7 days. Two patients who had developed hypoxia were also given 10 g/day of intravenous immunoglobulins and 1–2 mg/kg/day of methylprednisolone, both administered for 3 days. These two patients were also hooked to heated humidified high-flow nasal cannulas for 5 days, eventually recovering without complications.

There were no admissions to intensive care, and all included patients recovered fully and were sent home.

“In this report, we demonstrated 3.6 percent asymptomatic SARS-CoV-2 infection might take a turn for the worse,” the investigators said, adding that adequate detection of these cases was and remains a major roadblock for effective outbreak control.

“Those family members with fatigue and dry cough especially with fever were observed easily but asymptomatic members were ignored,” they added. “So, [a] large number of asymptomatic cases were actually a source of SARS-CoV-2 infection but [were] considered as ‘health[y] people’ before they were screened out.”

In a previous report, researchers from Henan, China, found evidence of asymptomatic transmission of SARS-CoV-2. Enrolling a familial cluster of 5 COVID-19 patients, the researchers traced back to find potential contacts. [JAMA 2020:doi:10.1001/jama.2020.2565]

They found an asymptomatic family member to be a potential carrier of the disease. Her temperature was normal and had no self-reported fevers nor gastrointestinal or respiratory symptoms. Chest CT imaging showed no abnormalities, and neither did her lab results.

Notably, she initially tested negative on reverse-transcription polymerase chain reaction (RT-PCR), though was found to be positive for viral RNA a couple of days later. Overall, her incubation period totaled 19 days, which was longer than usual, but fell within the reported range.

“Her first RT-PCR result was negative; false-negative results have been observed related to the quality of the kit, the collected sample, or performance of the test,” the Henan team said. “The mechanism by which asymptomatic carriers could acquire and transmit the coronavirus that causes COVID-19 requires further study.”