An Outbreak of Epidemic Keratoconjunctivitis Caused by Human Adenovirus Type 8 in Primary School, Southwest China

Background Two outbreaks of acute conjunctivitis occurred successively with an interval of five days in two boarding primary schools in Weixi Lisu autonomous county, Diqing Tibetan autonomous prefecture, Yunnan. The aims of this study were to determine the intensity of and characteristics of outbreaks, as well as the clinical manifestation of patients and risk factors infected, and the pathogen causing two outbreaks. Methods An outbreak investigation and a case-control study were conducted in two primary schools. The relevant specimens were collected by case definition, Next generation sequencing was adopted to identify the pathogen, and the epidemiological investigation method was used to analyze the related epidemiological characteristics such as risk factors. The phylogenetic tree was constructed by MEGA 7.0. Results A total of 331 acute conjunctivitis cases, as acute hemorrhagic conjunctivitis probable cases, were reported in two schools and the attack rates were 30.59% (171/559, 95%CI: 26.76-34.42) and 20.41% (160/784, 95%CI: 17.58-23.24), respectively. Cases occurred in all grades and classes in both schools, and only one staff was ill in each school. Epidemic situations lasted for 54 days and 45 days, respectively. Epidemic curve of two breaks appearing two peaks indicated the mode of person-to-person transmission for two outbreaks. The patients had typical manifestations of epidemic keratoconjunctivitis (EKC) such as acute onset, follicular hyperplasia, pseudomembrane formation, preauricular lymphadenopathy, corneal involvement and blurred vision, and the longer course of the disease (average 9.40 days, longest 23 days and shortest 7 days). The risk factor in infection was close contact with the patient or personal items contaminated by the patient. The pathogen caused the outbreaks is HAdV-8. The virus was highly homologous to the 2016 HAdV-8 strain in Tibet, China. Conclusions This study strongly suggests that HAdV-8 could lead to serious consequences. This is the second report of a HAdV-8 associated EKC outbreak in mainland of China. Tibetan HAdV-8 might be circulating in southwest China, it is necessary to monitor the pathogen of acute conjunctivitis in this area.