Presymptomatic transmission of COVID-19 in a cluster of cases occurred in confined space: a case report

Background : COVID-19 is spreading rapidly intercity and international despite rigid public health prevention and control measures been taken. Case presentation : In a cluster of infection, six out of seven participants engaged in persistent singing and talking in confined space were later diagnosed COVID-19 patients. One of the cases was asymptomatic with no SARS-CoV-2 nucleic acid detected, but positive for anti-SARS-CoV-2 IgG. None of the household contacts was infected during the following month. Conclusions : This epidemiological evidence revealed that asymptomatic patients transmitted the coronavirus in confined space with relatively high efficiency, suggesting that it is important to provide better ventilation in public buildings to prevent COVID-19 transmission.


Background
In December 2019, unexplained pneumonia cases were first identified in Wuhan, Hubei Province. These patients were later found to be infected with coronavirus disease-2019 (COVID-19), which quickly spread around in Hubei Province via person-to-person transmission (1). However, there is limited knowledge regarding the rapid transmission of COVID-19, presumed to be spread through respiratory droplets from coughs or sneezes (2,3). It is unclear whether the epidemically quicker spreading of COVID-19 infection in the current outbreak is due to more efficient person-to-person transmission.
Despite public health prevention and control measures been adopted, the COVID-19 infected patients increased exponentially in Wuhan after emerging, with 425 people infected and several health-care workers affected within a month (4). In January, many people who have travel history to Wuhan or direct contact with patients from Wuhan were diagnosed to be COVID-19 positive cases (1,5,6). Cluster of infections or outbreaks such as cluster in Diamond Princess Cruise, church-and hospital-associated clusters in South Korea took place in buildings with high population density but limited ventilation. To improve efficiency in public health prevention and control, investigating the epidemiologic characteristics and transmission dynamics of the sudden outbreak of COVID-19 is needed.

Case Presentation
We present a cluster of infection with six patients confirmed COVID-19 positive by Loudi Center for Disease Control and Prevention (CDC). The first case (case 1), living in Wuhan for the most of the time, attended activities with people crowded together for a consecutive of three days starting from Jan 10, 2020. Case 1 drove to Loudi, on Jan 14, 2020, together with case 6 and lived with the household of her mother-in-law for the following two days. Case 1 played cards with four distant relatives (cases 3-5 and relative 1) in a confined room in the evening of Jan 14, 2020. People who have been in contact with case 1 in a confined space are summarized in Table 1 with infected contact numbered after case and uninfected contact numbered after relative. Case 1 attended a party with a total of 224 people on Jan 15, 2020, and had lunch with eight friends and relatives.
Afterwards, case 1 went to Karaoke with five distant relatives and friends (case2-4, 6 and relative 1) in a confined room of 15 m 2 to sing songs for over two hours and gathered for supper. Notably, except for case 6, who drove case 1 to her mother's house, the people gather in the entertainment place did not see each other afterwards. Case 1 developed cough on Jan 17, 2020, however, she felt better after taking some traditional medicine prescribed by local village hospital. Case 1 lived with the household of her mother for the following days. Case 1 attended another party with 232 guests, however, none in the party was infected according to follow-up survey for over a month.
On Jan 23, 2020, case 1 got severe with dry cough and went to hospital. Symptom onset of the cluster case is shown in Figure 1  Consent for publication: Written informed consent was obtained from the patients for publication of this Case report. A copy of the written consent is available for review by the Editor of this journal.
Availability of data and materials: Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.

Competing interests:
The authors declare that they have no competing interests.