Room size is the major determinant for tuberculin conversion in health care workers exposed to a multidrug-resistant tuberculosis patient

Objective Transmission of Mycobacterium tuberculosis(MTB) to health care workers (HCWs) still representsa public health concern. A total of 71 obstetricworkers underwent contact tracing after recent workplaceexposure to a highly infectious multidrug-resistanttuberculosis patient [i.e., index case (IC)]. Aim ofthe study was to identify the main exposure predictorsfor the risk of conversion through evaluation of tuberculinscreening results.Methods HCWs were investigated by a questionnaire(community, occupational, IC exposure risk factors)and tuberculin skin test screening.Results Conversion was detected in 5 (8%) of the 63exposed workers and was not associated with eithercommunity or previous work-related risk factors.According to risk assessment, tuberculin conversionwas related to neither amount time of exposure, workshifts,nor number of contacts. Conversely, an exposureto the IC in diVerent hospital rooms was found signiWcantlydiVerent among converters compared to nonconverters( 2, P = 0.004). In particular, conversion wasassociated with exposure in two (obstetric emergencyroom, ambulatory discharge) out of the nine contactenvironments. Tuberculin conversion rates were associatedwith the room cubations of the exposure environments( 2 for trend, P < 0.01) and with worker age. In alogistic regression model adjusted for age, the lowerroom cubation was found the strongest predictor fortuberculin conversion (OR = 2.46, P = 0.02).Conclusion The study shows that the factors aVectingairborne mycobacterial dose (patient infectiousness,low sized conWned rooms) were the major determinantsfor MTB transmission after a brief exposure to ahighly infectious TB case.