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 represents a public health concern. A total of 71 obstetric workers underwent contact tracing after recent workplace exposure to a highly infectious multidrug-resistant tuberculosis patient [i.e., index case (IC)]. Aim of the study was to identify the main exposure predictors for the risk of conversion through evaluation of tuberculin screening 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 63 exposed workers and was not associated with either community or previous work-related risk factors. According to risk assessment, tuberculin conversion was related to neither amount time of exposure, workshifts, nor number of contacts. Conversely, an exposure to the IC in different hospital rooms was found significantly different among converters compared to non-converters (chi (2), P = 0.004). In particular, conversion was associated with exposure in two (obstetric emergency room, ambulatory discharge) out of the nine contact environments. Tuberculin conversion rates were associated with the room cubations of the exposure environments (chi (2) for trend, P < 0.01) and with worker age. In a logistic regression model adjusted for age, the lower room cubation was found the strongest predictor for tuberculin conversion (OR = 2.46, P = 0.02).

CONCLUSION

The study shows that the factors affecting airborne mycobacterial dose (patient infectiousness, low sized confined rooms) were the major determinants for MTB transmission after a brief exposure to a highly infectious TB case.