[The prevalence of latent tuberculosis infections among health-care workers--a three-country comparison]

Health-care workers are regularly screened for tuberculosis. To date, there has been no systematic analysis of the results of such a screening. A TB network for company doctors was created when interferon-γ release assays (IGRAs) were introduced in order to systematically collate their experience with IGRAs in preventive check-ups.

Data have so far been recorded from 2,028 preventive check-ups. There are also data from preventive check-ups in France (n=148) and Portugal (n=2,889) for the purposes of a combined analysis. QuantiFERON-TB® Gold In-Tube and the tuberculin skin test with RT23 were used in the three cohorts.

The prevalence of latent tuberculosis infections (LTBI) is dependent on age and country. Among young health-care workers (<25 years old), 3% had a positive IGRA in Germany, compared with 18% in Portugal. Among health-care workers aged 55 and over, 25% were positive in Germany and 45% were positive in Portugal. In the French cohort an increase from 23% to 33% was observed when the youngest and oldest age categories were compared. Active tuberculosis has so far been diagnosed in 12 health-care workers in Portugal, four of whom developed culturally confirmed TB within the first two years following a positive IGRA. The risk of progression subsequent to a positive IGRA was 0.2% per annum.

There is a low prevalence of LTBI among young health-care workers. In them a positive IGRA following close contact with an infectious patient is likely to indicate recent infection. Apart from that, older infections appear to prevail, as the IGRA results depend greatly on age, and the risk of progression following a positive IGRA appears to be low in the study groups. A positive IGRA should therefore be interpreted with caution as an indication of the need for chemotherapy.