No 26 - 2022

Typhoid and paratyphoid fever infection 2019-2021

Typhoid and paratyphoid fever infection 2019-2021

Typhoid and paratyphoid fever is caused by the Gram-negative rod-shaped bacteria Salmonella Typhi or Salmonella Paratyphi A, B or C. These Salmonella bacteria may produce serious systemic infections, which often present with symptoms like fever and diarrhoea. If left untreated, these conditions have an approx. 10% mortality. Salmonella Typhi and Salmonella Paratyphi infections are individually notifiable to Statens Serum Institut (SSI). Notification is done by the treating physician via the Danish Health Data Authority’s Electronic Notification System (SEI2) which has now replaces paper form 1515. Additionally, laboratory findings of S. Typhi/Paratyphi are monitored through the national laboratory monitoring system. Using the information received from the laboratories and from the treating physicians, the SSI monitors trends in the prevalence of typhoid and paratyphoid fever in Denmark.

The number of cases of S. Typhi and S. Paratyphi infection has followed a decreasing trend in the 2019-2021 period. A detailed 2019-2021 annual report is available here. Typhoid and paratyphoid fever are generally considered imported conditions as the overwhelming share of persons become infected during travels abroad; to the Indian subcontinent, in particular. The observed decline in the number of cases is therefore likely owed to reduced travelling activity following the introduction of travelling restrictions during the COVID-19 pandemic. The overview of monitoring data presented as figures, graphs and maps shows the decline in the number of cases compared with previous periods.

Typhoid and paratyphoid fever are primarily transmitted through ingestion of food or water that has become contaminated with faeces from people who carry S. Typhi or S. Paratyphi in their intestines. Once an individual has become infected by S. Typhi or S. Paratyphi, he or she may become a chronic carrier who may secrete the bacterium in the faeces for more than a year. The Danish Patient Safety Authority (DPSA) may impose special requirements regarding negative rectal swabs/faeces samples on persons who, e.g., are employed in the food industry or regarding children who attend a child-care facility before they may resume work or contact to their care facility.

In the period from 2019 to 2021, a total of 47 cases of S. Typhi and S. Paratyphi were recorded. Only half of the laboratory-confirmed cases were notified clinically. Clinical notifications often include information about the disease course and other information that may underpin monitoring efforts. To take an example, the country of infection is more frequently stated in the clinical notifications than in cases notified via the laboratory system.

According to the clinical notifications, two cases were presumably infected in Denmark. Infection within Denmark is unlikely but not impossible. Nearly half of the clinically notified cases were notified as infected in Pakistan and 20% in Cambodia. Other countries of infection were India, Iraq, Iran, Kenya, Morocco, Uganda, Indonesia, Brazil and Bangladesh.

Whole genome sequencing has formed part of the national Salmonella laboratory monitoring since 2017. By mutual comparison of the genomes of the bacteria, it can be established how likely two persons are to have become infected by the same source. In the 2019-2021 period, whole genome sequencing allowed for identification of S. Typhi/S. Paratyphi isolates related to a total of six minor travel-related clusters, possibly reflecting that the persons in each cluster had become infected by the same source.

In Denmark, empirical treatment of patients admitted with typhoid fever is ceftriaxone, a third-generation cephalosporin. In the 2019-2021 period, four cases with resistance to third generation cephalosporins were registered. Three of these cases had been notified with Pakistan as the presumed country of infection, whereas the country of infection was unknown for the final case. This corresponds to one third of the bacteria isolates from S. Typhi cases imported from Pakistan not being susceptible to ceftriaxone.

As most typhoid fever cases registered in Denmark occur among persons who, e.g., are visiting relatives in areas of the world where typhoid fever is endemic, we suggest providing typhoid fever vaccination for these persons before they embark on their journeys, regardless of the travel duration. Risk areas include, e.g., Pakistan, which is also the most frequently recorded country of infection in the period covered by the present report, and currently the only country from which we are recording XDR S. Typhi. Additionally, it may be relevant to consider vaccination in other situations, e.g., if you will be staying in an endemic area for more than two weeks, primarily on the Indian Subcontinent, or if the conditions during the travel may be expected to place the traveller at risk of ingesting contaminated water. Typhoid fever vaccination is not effective for prevention of paratyphoid fever, even though some cross-protection has been described when using the live attenuated vaccine, which is administered orally.

(T. Larsen, Department of Infectious Disease Epidemiology and Prevention and P. Gymoese, Department of Bacteria, Parasites and Fungi).

29 June 2022