[Frequency Distribution and Risk Factors for Latent Tuberculosis in Contact Persons: Cologne 2012-2016]

As part of tuberculosis control and the WHO end-TB strategy, contact persons of tuberculosis patients in Germany are examined for a possible infection with latent tuberculosis (LTBI). Activation of LTBI contributes a considerable proportion of newly reported tuberculosis cases in low-incidence countries such as Germany. Therefore, the aim is to detect cases of LTBI and, through chemopreventive treatment of these cases, prevent future, post-primary, active tuberculosis.In Germany, the rate of LTBI among contact persons of people diagnosed with active tuberculosis is not systematically recorded. The aim of the present work was to close this data gap for Cologne, a major city in Germany with a TB incidence of around 9/100,000 in the past years. The study further aimed to describe risk factors for LTBI and to reevaluate the standard inclusion criteria for contact investigation for tuberculosis under routine conditions in Germany.

For the period 07/2012 to 12/2016, the retrospective cohort study examined the rate of LTBI diagnoses among contact persons of those with pulmonary tuberculosis notified at the Cologne public health department, as well as factors that increase the LTBI infection risk of contact persons. The diagnosis of latent tuberculosis was made when the interferon-gamma release assay (IGRA) was positive and there were no signs of active tuberculosis. The study included contact persons who cumulatively had a previously defined minimum total contact time with a tuberculosis patient, who were at least 5 years old at the time of the study and who were registered in Cologne. Statistical evaluation was carried out descriptively as absolute and relative frequency with a significance level of p ≤ 0.05. The analytical evaluation was carried out with univariate and multivariate logistic regression.

Of a total of 3862 IGRA examinations among contact persons, 2834 cases met the inclusion criteria. A median of seven contact persons per index patient was reported. 12.5 % ​​of the study group tested positive for LTBI. In contact persons of microscopically open index patients, the positivity rate was 11.4 %, in culturally open but microscopically negative index patients, it was 14.3 %. Factors associated with a higher risk of LTBI included male sex (OR = 1.95), age ≥ 50 years (OR = 1.8) and household exposure (OR = 2.37).

Using the German standard criteria, the positivity rate of IGRA testing and the diagnosis of LTBI among contacts in the present study was 12.5 %, which is lower than in other similar studies. Factors identified in the cohort for an increased risk of LTBI confirm known constellations. The significantly higher positivity rate among contact persons of microscopically negative but culturally positive index patients (p = 0.033) underscores the need to conduct a detailed contact examination of individuals of this group as well.