Estimation of environmental control measures for tuberculosis transmission in care facilities for the elderly

Exogenous reinfections in tuberculosis (TB) have been reported among elderly patients in long-term care facilities. This study estimated the impact of upper room ultraviolet germicidal irradiation (UVGI) and negative air ionization on the reduction in TB infection assuming that current TB control failed.

Estimated probability distributions RA, RM, RUV+M, and RIO+M, denoting the reproduction numbers of cases with no intervention, wearing surgical mask of infector, upper room UVGI, and negative ionization with wearing mask, respectively were determined.

It was assumed that 1 TB patient and 29 susceptibles stayed for 10 hours per day when ACH was 3; all subjects stayed for 60 consecutive days. The median RA increased from 7.38 (15th day) to 11.72 (two month). The percent reductions of RM, RUV+M, and RIO+M ranged from 52.4% (15th day) to 41.6% (two month), from 76.6% to 68.3%, and from 74.9% to 63.0%, respectively. The percent reductions of slopes; the change of median RM, RUV+M, and RIO+M for a change in length of stay, were estimated to be 50.8%, 87.3% and 73.7% when ACH was 1.

In addition to case detection and source control measures, environmental control measures may be effective in preventing exogenous reinfection of TB in elderly care facilities.