From: https://www.contagionlive.com/news/case-study-shows-asymptomatic-transmission-of-covid19-in-china
BY JONNA LORENZ
A case study of a family in Zhejiang Province, China, shows how COVID-19 disease can spread before symptoms of the disease appear, and symptoms can vary widely even within a close family group.
The study, published in Clinical Infectious Diseases , details how SARS-CoV-2 spread from a presymptomatic carrier to infect 8 of 9 family members in 3 households after a 58-year-old woman (index 1) and a 60-year-old man (index 2) attended a Spring Festival temple activity in China on January 19.
Researchers from Ningbo Hospital and Nottingham University Ningbo, China, in Zhejiang Province, examined the case for the study, which was funded by the Zhejiang Provincial Natural Science Foundation.
Among the patients who contracted the disease, 2 remained asymptomatic and 1 was placed in intensive care with severe pneumonia.
The index couple's daughter (case 1), son-in-law (case 2), and two grandchildren, aged 6 years (case 3) and 13 months (case 4), visited the couple after the festival but before the onset of symptoms, from January 20-23. On January 23, the young family (cases 1-4) visited the mother (case 5), father (case 6), and grandmother (case 7) of case 2.
Index 1 developed symptoms of headache, fatigue, and fever on January 24, went to the hospital on January 26, and was diagnosed with COVID-19 on January 29. Following the diagnosis, the patient's husband and the four family members who had stayed with them were hospitalized for observation. Her husband remained asymptomatic but tested positive for the virus on February 1. Case 1 began experiencing fever and a cough on January 27, and Case 2 developed a fever on February 1.
The 6-year-old girl was the only member of the family who had not been diagnosed with SARS-CoV-2. The other child, a 13-month-old girl, tested positive for the virus on February 5, but was asymptomatic.
The third household member of the family was admitted to the hospital for observation on February 1 and subsequently tested positive. Case 6, a 57-year-old man, was transferred to the intensive care unit on February 11 when his condition worsened.
The case study demonstrates that COVID-19 is clinically diverse, transmissible during the incubation period, and can result in infected patients experiencing no symptoms. The study found that viral loads were similar between symptomatic and asymptomatic patients.
"These 'silent patients' may remain undiagnosed and be able to transmit the disease to a large number of people," the study noted.
"In summary, there are variations among individuals in the clinical manifestations of COVID-19. According to our reports, we must pay attention to how to prevent people from becoming infected with asymptomatic patients and patients who were in their incubation period."
The incubation period for COVID-19 is estimated to be 5 days on average, with 97.5% of patients developing symptoms within 11.5 days of infection, a recent study showed .
The large number of patients infected with the virus who show few or no symptoms, estimated to be as high as 80%, complicates the fight against the disease, forcing health workers around the world to shift their focus from containing the disease to mitigation, a recent report noted .
To assist providers in this effort, the National Institutes of Health have added a section to their website to provide training to people at risk of exposure to the virus on techniques, policies, and procedures to help reduce risk.