Investigation of an outbreak of co-infection of influenza B virus and human rhinovirus in a primary school in Huzhou, Zhejiang

  Objective   To understand the epidemiological characteristics of an outbreak of respiratory tract infection caused by co-infection of influenza B and human rhinovirus in a primary school in Huzhou, Zhejiang province, and provide scientific reference for the prevention and control of school outbreaks caused by co-infection of influenza B and human rhinovirus in the future.

  Methods  The investigation was carried out according to the Guidelines for Response to Influenza Like Illness Outbreaks (2018 edition).The throat swabs of the cases were collected for the nucleic acid detectios of influenza A and B virus, adenovirus, human metapneumo virus, Boca virus, respiratory syncytial virus and human rhinovirus.

  Results  A total of 99 respiratory tract infection cases were found. The clinical manifestations of the cases were mainly cough, sore throat and fever. Some cases had fatigue, dizziness, headache and other symptoms. The first case occurred on February 18, 2022, and the cases mainly occurred from February 21 to February 28 and the last case occurred on March 25. The outbreak lasted for 36 days. The cases were all students in grades 1-3. The overall attack rate was 36.80% (99/269), the attack rate was 43.04% in class 103(19/45), 13.64% in class 105 (6/44), 65.91% in class 201 (29/44), 15.56% in class 202 (7/45), 72.73% in class 203 (32/44), and 13.04% in class 308 (6/46). No cases were found in other classes. The difference in attack rate among classes were significant (χ²=71.570, P＜0.05). The attack rate was 40.88% in boy students (56/137) and 32.58% in girl students (43/132), the difference was not significant (χ²=0.480, P＞0.05). A total of 53 throat swabs were collected from the cases, in which 7 were positive for nucleic acid of influenza B virus Victoria lineage, 18 were positive for nucleic acid of human rhinovirus, and 6 were positive for multiple viruses; The positive rate of influenza B virus Victoria lineage was 24.53%, and the positive rate of human rhinovirus was 45.28%.

  Conclusion  The clinical symptom of the cases at the initial stage of the outbreak was mainly fever, indicating a typical influenza outbreak, but the proportion of fever cases gradually decreased over time. The cases at the later stage of the outbreak mainly had common cold symptom. Laboratory tests confirmed that the cases at the initial stage of the outbreak were infected with influenza B virus, the cases at the middle stage were infected with influenza B virus and human rhinovirus, and the cases at the later stage were infected with human rhinovirus. Therefore, when the clinical symptoms and signs of new cases change at different stages of an outbreak, co-infection of two or more pathogens can be considered.