Sewage workers with low antibody responses may be colonized successively by several Tropheryma whipplei strains

• Sewage workers can be asymptomatic carriers of Tropheryma whipplei.
• Asymptomatic carriage can be chronic (up to 7 years).
• Carriers with a strong immune response to T. whipplei seem to be protected.
• Carriers with low antibody levels may be re-colonized by another strain.

SummaryObjectivesAsymptomatic faecal carriage of Tropheryma whipplei, the agent of Whipple's disease, is reported among sewage workers. However, the potential development of such carriage is unknown. A 7-year follow-up of T. whipplei-carrying sewage workers is reported.MethodsNineteen sewage workers previously detected as faecal carriers of T. whipplei were followed to ascertain the chronicity of their carriage. Faeces were tested by molecular assays using quantitative real-time PCR specifically targeting T. whipplei. Serological anti-T. whipplei Western blotting was also performed.ResultsSeventy-nine percent (15/19) of workers exhibited a strong immune response against T. whipplei. Among these, five were followed for more than 1 year. Four maintained a strong response, with three carrying the same strain and one becoming negative. The fifth exhibited a decreased immune response, a negative faeces result, and subsequent carriage of another strain. Three individuals with low immune responses were also followed. Two never developed a response, with one carrying the same strain and one becoming negative and then positive with another strain; the third developed a strong response and became negative.ConclusionsChronic T. whipplei carriers appear to be protected against reinfection, but those with low or decreasing antibody levels may be re-colonized by another strain.