Objective To understand the epidemic scope, source of infection, route of transmission and risk factors of an outbreak of typhoid fever in Beijing in 2022, take preventive and control measures, and provide suggestions for the prevention of similar outbreaks in the future.

Methods The case definition was developed and case finding was conducted. Typhoid case investigation form was used to collect case information. The electronic payment records of all cases within 14 days before the onset of all cases were collected for an analysis combined with interview data, including the information about the shops where the patients purchased food and food delivery workers. People who had travel history in Sindh of Pakistan or contacts with such cases, were screened for index case. The information about apartment residents were collected by questionnaires, and the risk factors were investigated by case-control study. Environmental hygiene and water supply investigations were carried out, and household samples, drinking water samples and environmental smears were collected for Salmonella typhi detection. The antibiotic sensitivity test and whole genome sequencing of S. typhi strains isolated from blood of some cases and water samples were carried out.

Results A total of 27 cases of typhoid fever occurred in the north building of the apartment, the attack rate was 25.47% (27/106), and the cases mainly occurred between January 20 and February 14, 2022, with a peak on February 4. All the cases were migrant workers from other areas. The results of the case-control study showed that drinking unboiled water was a risk factor odds ratio (OR)=4.13, 95% confidence interval (95%CI): 1.16−14.69, χ²=5.270, P=0.022. Hygienic investigation suggests that the drinking water of north building was highly contaminated. Salmonella typhi isolated from the blood samples of 4 cases and 1 overflow water sample from the water tank of north building were resistant to ampicillin, chloramphenicol, trimethoprim sulfamethoxazole, amtronam, streptomycin, fluoroquinolones, third and fourth generation cephalosporins, The whole genome sequencing indicated that the strains from the blood samples of the cases and the strains from water samples belonged to the same sequence type.

Conclusion This was an outbreak of typhoid fever caused by the contamination of drinking water by Salmonella. The outbreak revealed the problems in the management and supervision of secondary water supply systems of self-built rental apartments. It is necessary to strengthen the standardized and adequate disinfection of drinking water and regular supervision of water supply network to ensure the safety of drinking water and prevent such epidemics.