Epidemiological investigation of a COVID-19 family cluster outbreak transmitted by a 3-month-old infant

Objective: To investigate the clinical characteristics, epidemiological characteristics, and transmissibility of coronavirus disease 2019 (COVID-19) in a family cluster outbreak transmitted by a 3-month-old confirmed positive infant. Methods: Field-based epidemiological methods were used to investigate cases and their close contacts. Real-time fluorescent reverse transcription polymerase chain reaction (RT-PCR) was used to detect Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) for all collected specimens. Serum SARS-CoV-2 IgM and IgG antibodies were detected by Chemiluminescence and Gold immnnochromatography (GICA). Results: The outbreak was a family cluster with an attack rate of 80% (4/5). The first case in this family was a 3-month-old infant. The transmission chain was confirmed from infant to adults (her father, mother and grandmother). Fecal tests for SARS-CoV-2 RNA remained positive for 37 days after the infant was discharged. The infant's grandmother was confirmed to be positive 2 days after the infant was discharged from hospital. Patients A (3-month-old female), B (patient A's father), C (patient A's grandmother), and D (patient A's mother) had positive serum IgG and negative IgM, but patients A's grandfather serum IgG and IgM were negative. Conclusion: SARS-CoV-2 has strong transmissibility within family settings and presence of viral RNA in stool raises concern for possible fecal-oral transmission. Hospital follow-up and close contact tracing are necessary for those diagnosed with COVID-19.