Objective  To describe family clustering characteristics of novel coronavirus disease 2019 (COVID-19) and to explore the transmission mode of the emerged novel coronavirus (2019-nCoV).

  Methods  We conducted field and questionnaire surveys among 7 laboratory confirmed COVID-19 cases and an asymptomatic infection and 123 close contacts of the cases from February 1 – 16, 2020 in Fengjie, Chongqing. All the cases′ and the asymptomatic infection′s throat swab specimens were viral nucleic acid positive with real-time reverse transcription PCR (RT-PCR).

  Results  The 7 confirmed cases and an asymptomatic infection were from 3 relative families; five members of the first case′s family were long-term immigrants of Wuhan city – the epicenter of the disease outbreak and histories of cohabitation and frequent home party immediately after the migrant family returning to Fengjie county from Wuhan city was reported by the members of the other two families. The first case was a 37-year old man diagnosed on February 1, 2020 at Fengjie county 8 days after leaving Wuhan and 7 days after the occurrence of clinical symptoms; the man′s son and the man′s father and mother were diagnosed 10 days and 11 days after the confirmation of the first case. One the same day of the first diagnosis, the second case – a 41-year old man (the first case′s brother in law) was also diagnosed 7 days after having dinners together with the first case and 4 days after the onset of symptoms; ten days after the diagnosis, the second case′s father and mother were diagnosed as confirmed cases and his wife was diagnosed as a suspected case 11 days after the diagnosis of the second case. Totally 123 close contacts of the first and the second case were identified but no close contacts of other cases were reported. No COVID-19 associated clinical symptoms were observed during 14 day′s medical observation among all the close contacts. The estimated infection rate among the members of the three families was 72.7%.

  Conclusion  The study confirmed a close contact associated family cluster of novel coronavirus disease 2019 in Fengjie county Chongqing municipality and the study results suggest that droplet transmission and close contact are main transmission ways of the novel coronavirus.