![[ Visit Client Website ]](images/banner.png)
BACKGROUND: Tuberculosis (TB) is transmitted from person to person through the airborne route. Homeless shelters are of special concern for TB transmission because of their crowded sleeping environments and vulnerability of the hosts for progression to active disease after TB exposure. Public Health – Seattle & King County initiated an investigation after a homeless shelter client in King County, Washington was diagnosed with active pulmonary TB. We conducted a case-control study to determine if TB infection was associated with the number of nights an individual spent at the shelter while the index case was contagious.
METHODS: We attempted to locate, evaluate, and provide treatment to shelter clients who were potentially exposed to the index case. Data on number of nights exposed for each contact were obtained from shelter management; data on age, place of birth, and clinical TB status (active TB disease and latent TB infection [LTBI]) was determined based on clinical assessment including symptom review, chest radiograph, and interferon gamma release assay (IGRA) testing. Cases were defined as persons diagnosed with clinical TB infection, while shelter clients who were asymptomatic with negative IGRA were defined as controls. Cases were matched 1:1 by age to controls. Conditional logistic regression was used to determine the association between nights exposed and TB infection. Place of birth was assessed as a possible confounder. Odds ratios (OR) and accompanying 95% confidence intervals (CI) were calculated using a significance level of α=0.05.
RESULTS: Of 101 exposed shelter contacts identified, 67 were evaluated using IGRA (66%). Thirty-six persons were negative for active TB disease and LTBI. Overall, 31 (31%) contacts were found to have clinical TB infection. Matching resulted in 31 case-control pairs. The case-control study found that number of nights exposed was associated with TB infection (p=0.0507), an association that became stronger after adjusting for birthplace (p=0.0326). The odds of being diagnosed with TB infection increased by 3% for every night an individual was exposed to the index case (crude OR = 1.03, 95%CI = 1.00-1.05). After adjusting for place of birth, the odds of TB infection increased by 6% for every night exposed (adjusted OR = 1.06, 95%CI = 1.01-1.12).
CONCLUSIONS: Number of nights exposed to the index case in a homeless shelter setting was a significant risk factor for TB infection. Public health officials can consider using number of nights exposed to prioritize contact investigations in future tuberculosis exposures in similar congregate settings.