Investigation of an outbreak caused by adenovirus type 3 in a school of Shenzhen, Guangdong, 2023

Objective To investigate the epidemiological and etiological characteristics of an outbreak of adenovirus type 3 infection in a school in Shenzhen, Guangdong province, in 2023.

Methods Field epidemiological investigation was conducted, and the possible risk factors were analyzed by descriptive epidemiological method and case-control study. Throat swabs were collected to detect common respiratory viruses by fluorescence quantitative polymerase chain reaction. The adenovirus nucleic acid positive samples were amplified for gene sequencing, and the sequencing results were subjected to sequence alignment based on GenBank to determine the virus subtype and conduct phylogenetic analysis.

Results A total of 44 cases were identified in the outbreak, of which 27 were suspected cases and 17 were confirmed cases. All the cases were students aged 6−9 years, with a median age of 7.50 years. In the 44 cases, 24 were boys (attack rate: 2.48%) and 20 were girls (attack rate: 2.25%), and there was no significant difference in the attack rate between boys and girls (χ²=0.105, P=0.745). All the cases had fever symptom. In the the confirmed cases, 47.06% (8/17) had fever above 39 ℃, 64.71% (11/17) had respiratory symptoms, such as cough and sore throat, and 52.94% (9/17) had gastrointestinal symptoms, such as vomiting and diarrhea. The clinical samples from 15 confirmed cases were tested positive for adenovirus B subgenus type 3. Phylogenetic tree results showed that the hexon gene sequences of the isolates shared 99.54% homology with the strains isolated from Guangzhou, Chongqing and other areas. The degree of genetic variation was small. The results of the case-control study showed that hand washing without using sanitizer or soap after general cleaning was an independent risk factor for this outbreak (odds ratio=6.37, 95% confidence interval: 1.04−39.15).

Conclusion It was a school outbreak caused by adenovirus B subgenus type 3, which might be transmitted indirectly by hand contamination. Attention should be paid to student hand hygiene and early diagnosis, isolation and reporting of human adenovirus infection cases.