SARS-CoV-2 broke out in Wuhan near December 2019, Guizhou Provence launched the first level response to major public health emergencies at 24th January 2020, Zunyi implemented social control immediately to inhibit SARS-CoV-2 transmission [9]. But under social control, family aggregated infection appeared obviously. Extensive screening and separated isolation were made up, and proven to be effective. The last SARS-CoV-2 positive patients were found by screening at 15 February 2020, and until 3 March 2020, there wasn’t new SARS-CoV-2 case found in Zunyi. There was no medical staff with 3-level biosafety protection being infected.
SARS-CoV-2 family aggregated infections were reported dispersedly mainly by only one family, data for comprehensive family aggregated infection analysis was limited [15,16]. In this study, we analyzed family aggregated infection in 10 families. Without self-isolation, chance of family close contacts being infected was 50.98% (24/46); the infection risk in family members close contacts was much higher than that of non-family members and all close contacts ( shown in Table 3 and Table 4).
People from epidemic focus should be key monitoring and isolation objects. Patient 05 and patient 08 came back from Wuhan, but had not performed self-isolation, caused serious family aggregated infection. Especially patient 05 came back from Wuhan at 21th January 2020, infected 8 family members; nevertheless, patient 05 did not have clinical symptoms (observation deadline 3 March 2020), it is difficult to find him out by clinical symptoms. On the other hand, patients 01, 02 and 03 were also from epidemic focus, but performed self-isolation, and did not infected anybody else. So self-isolation was effective complementary mean for social control.
According to published researches and guidelines for SARS-CoV-2 diagnosis and treatment, fever was the main early clinical screening symptoms for SARS-CoV-2 [10, 12]. We screened 3249 patients with fever, found 9 (9/3249) SARS-CoV-2 positive cases only. In all SARS-CoV-2 positive patients of this study, positive cases with fever was only 25.71% (9/35), positive cases with fever and other early clinical symptoms were 37.15% (13/35). However, asymptomatic infections (62.86%, 22/35) were the main part of SARS-CoV-2 positive patients. Asymptomatic SARS-CoV-2 positive patient (patient 05) was proved to be infectious. Although it is convenient to distinguish SARS-CoV-2 high risk groups by temperature, a large part of asymptomatic SARS-CoV-2 carriers will be missed. So extensive screening was needed to find out asymptomatic infections.
In previous studies, basic reproduction number (R0) of SARS-CoV-2 was calculated to be near 2.2 by models, meaning that every SARS-CoV-2 positive patient can spread infection to 2.2 other people on average [12]. In this study, we found that one SARS-CoV-2 positive patient infected 2.08 (25/12) people on average under social control without separated isolation, meant effective number of SARS-CoV-2 infection was 2.08 under only social control, it was still high. Separated isolation and extensive screening were still needed.
The results of the study had positive effect on the prevention of SARS-CoV-2. This study was performed under the measures of the first level response to major public health emergencies; the characteristics of SARS-CoV-2 can not represent all status under different interventions.