Use of a mathematical model to estimate tuberculosis transmission risk in an Internet café

People who live under fragile living conditions may stay overnight in Internet cafés in urban areas. An outbreak of tuberculosis (TB), the routes of which were possibly related to such a facility, has been reported. The purpose of this study was to use a mathematical model to quantify the public health risk of TB infection in such a facility.

The reproduction number for airborne infection in an enclosed space (R (A)) was estimated using a Wells-Riley model. First, we estimated R (A) for the TB infection based on the report of the TB outbreak in the Internet café. Second, TB infectious dose, number of days of exposure, and air-exchange rate in the facility were varied to estimate the effect of TB risk settings and environmental factors.

We assumed that TB patients and 59 susceptible subjects stayed for 150 days in a room where the air-exchange rate was five per hour. Using the estimated median R (A) of 44.14, the TB infection rate was 74.6%. This result was similar to the epidemiological report that the TB infection rate among employees in the Internet café was 70%. The median R (A) increased linearly as the number of days of exposure increased. The slope of the change in median R (A) divided by the change in the number of days of exposure increased exponentially as air-exchange rate decreased; thus air ventilation in a facility may be essential to prevent TB infection.

Appropriate air ventilation in facilities such as Internet cafés is needed as part of a TB-control program in metropolitan areas.