On February 6, 2022, an unusual infection event was noticed by hospitals and Beijing CDC: 4 clinically diagnosed typhoid cases (3 in Beijing, 1 in Chifeng City, Inner Mongolia Autonomous Region) were reported to China’s Infectious Disease Information System. The detailed epidemiological investigation was initiated by Changping District CDC. This outbreak involved 23 cases in an apartment in Changping District in Beijing and was caused by extensively drug-resistant (XDR) Salmonella Typhi (S. Typhi) through polluted water supply, which was confirmed by laboratory detection.
Based on the epidemiological curve by date of onset and spatial distribution of cases, a point outbreak was suggested. Considering the possibility of foodborne infection, we checked the dietary history of these cases for 14 days prior to onset, but no evidence of common food or dining together was found to support this. We did not conduct case-control studies, but we received information that most cases keep good hygiene in water usage: they did not drink raw water, but they used tap water to wash vegetables and brush teeth. During this survey, the residents reported that the household water had an odor for about half a month in late December 2021, and some reported that there was disruption of water supply and transient muddy water in mid-January 2022. Herein, the water supply in this apartment was further investigated. The domestic water was supplied from a self-provided well in the village, which was piped to six apartments including the apartment where the cases lived in. Water was pumped from a nearby branch well to storage tank on the roof of the apartment for 24 hours a day to ensure adequate water supply, and then distributed to each room. In field investigation, we learned that sewage pipeline reconstruction work was carried out in December 2021 near the apartment, and the sewage pipeline was just about 1 meter away from the branch well which supplied water for the apartment.
In summary, this was the first report of waterborne outbreak caused by XDR S. Typhi in China. Whole-genome comparison and drug resistance analysis indicated that it belonged to H58 lineage 220.127.116.11.P1 originating from Pakistan, which had the capacity to invade and spread globally by travel-associated international transmission, with the potential to replace native strains (4). However, it was unclear how this novel clone strain entered China and was associated with this outbreak, due to the lack of detailed historical epidemiological data. Importantly, in a modern city such as Beijing, especially in suburban or rural areas where the municipal water supply does not reach, there is still a potential risk of typhoid fever outbreak. So, it is urgent to appeal to relevant governmental authorities to provide safe and hygienic potable water, strengthen supervision on water quality, and educate the public to keep good hygiene habits. In addition, with narrow treatment options for typhoid fever, XDR typhoid itself should also attract great attention, which may lead to treatment failure, prolonged hospitalization, as well as recurrent and extensive transmission of the disease. Therefore, it is necessary to track the source of the XDR strains and to strengthen monitoring their spread through laboratory and extensive epidemiological investigations in the future.