Persons in contact with pulmonary tuberculosis [TB] patients are at increased risk of both latent tuberculosis infection [LTBI] and TB compared to the general population [1]. Therefore, public health follow-up and contact investigation of all patients with active TB is strongly recommended [2],[3]. Identifying and controlling infection sources through contact tracing reduces morbidity and mortality through early detection of new TB cases, detection of TB outbreaks, and elimination of transmission [4],[5],[6],[7].

The risk of TB among contacts may be related to the characteristics of the index cases, the contacts themselves, or the environment where the exposure occurred. Positive sputum smear microscopy and cavitary lesions in the index case may favour the emission of large volumes of bacteria and increase the transmission risk [8],[9]. In addition to age and sex of contacts, immigration from high TB endemic countries is a widely studied risk factor, given that unfavourable social and economic conditions during the first years of the migration process in host countries may increase the risk of TB [10],[11]. Some studies have also reported that TB risk is greater among contacts who smoke [12],[13]. Exposure time to the index case may be a greater determinant of LTBI and TB risk [14],[15]. However, exposure time recording and assessment is not standardized and empirical evidence is weak [7],[16].

In Catalonia [Spain], a community with some seven million inhabitants and a TB annual incidence rate of 10 cases per 105 inhabitants, epidemiology services and TB clinical units identify exposed individuals by implementing TB contact studies [17]. Understanding the factors associated with TB, including exposure time to index cases, can help improve criteria for studying and treating contacts [18].

The aim of the study was to determine the role of exposure time to pulmonary TB index cases on the risk of TB among their contacts, taking into account other risk factors in both, cases and contacts.