Re-infection of typhoid fever and typhoid vaccine (comment on “An imported enteric fever caused by a quinolone-resistant Salmonella typhi”)

To the Editor: I read with interest the case report “An imported enteric fever caused by a quinolone-resistant Salmonella typhi[sic]” by Somily et al¹ and have the following comments:

The patient described in the case had two episodes of typhoid fever two months apart. The authors have labelled the second infection as a relapse. However, relapse usually occurs two to three weeks after the resolution of fever and is known to occur in 5% to 10% of patients.² It is usually milder than the original attack, and the S Typhi strain isolated in relapse usually has the same antibiotic susceptibility pattern as the isolate during the original attack. Although rare, re-infection may also occur and can be distinguished from relapse by molecular typing.³,⁴ The patient in the case seems to have re-infection with S Typhi.

I would like to know whether the patient was already immunised with typhoid vaccine before the first attack. If not, I would also like to ask the authors whether typhoid vaccination in the patient after the first attack would have prevented the re-infection. Centers for Disease Control and Prevention (CDC) recommend typhoid vaccine for travelers to areas where there is a recognized increased risk of exposure to S Typhi. As observed with many bacterial diseases, an attack of typhoid fever does not provide long lasting immunity from a future episode of the same illness. An episode of typhoid fever usually means that the child lives in an environment in which further exposure to infection is likely. There is also the possibility that early treatment would have reduced the full force of immunity from developing. Trials have shown that treatment of typhoid patients in the first two weeks of illness may inhibit the development of the protective anti-Vi CPS antibody response.⁵ Taking into consideration the above points, the general recommendation is to give typhoid vaccine at least 4 weeks after full recovery from the illness.