Community infection ratio as an indicator for tuberculosis control in Zambia : a case-control study of purified protein derivative among house-holds contacts of confirmed pulmonary tuberculosis and control uses

Abstract

The epidemiology of tuberculosis in Zambia is poorly understood. The study investigated the relative importance of transmission within the household and in the community among children aged 2 years to 12 years living in the shanty-townships lusaka, Zambia. The prevalence of Mycobacterium tuberculosis exposure among contact children (living in a household where there was a named case of pulmonary TB) and 183 control children (living houses nearby free of active tuberculosis) was defined as the portion of children with a positive tuberculin skin test. 23 (22%) contact children and 48(36%) controls were tuberculin positive. Living in a contact household, was not a factor for tuberculin positivity (OR 0.33; 0.06 - 1.84; 95% However, age was a risk factor for tuberculin positivity 0.40; 0.24 - 0.95, 95%) Cl). Amount of bacilli in the sputum was a risk factor for tuberculin reactivity (OR 5.63; 1.59 - 21.78; 95% Cl). additional status was also a risk factor for tuberculin .activity (OR 2.13; 1.03 - 4.40; 95% Cl). The community infection ratio (CIR) was calculated as the 3 ratio of tuberculin controls to tuberculin contacts (2): CIR= Prevalence in controls/(1-Prevalence in controls) Prevalence in contacts/(1-Prevalence in contacts) The epidemiology of tuberculosis in Zambia is poorly understood. The study investigated the relative importance of TB transmission within the household and in the community among children aged 2 years to 12 years living in the shanty-townships of Lusaka, Zambia. The prevalence of Mycobacterium tuberculosis exposure among 106 contact children (living in a household where there was a confirmed case of pulmonary TB) and 183 control children (living in houses nearby free of active tuberculosis) was defined as the proportion of children with a positive tuberculin skin test. 23 (22%) contact children and 48(36%) controls were tuberculin positive. Living in a contact household, was not a risk factor for tuberculin positivity (OR 0.33; 0.06 - 1.84; 95% Cl). However, age was a risk factor for tuberculin positivity (OR 0.40; 0.24 - 0.95, 95%) Cl). Amount of bacilli in the sputum was a risk factor for tuberculin reactivity (OR 5.63; 1.59 - 21.78; 95% Cl). Nutritional status was also a risk factor for tuberculin positivity (OR 2.13; 1.03 - 4.40; 95% Cl). The community infection ratio (CIR) was calculated as the odds ratio of tuberculin controls to tuberculin contacts (2): Prevalence in controls/(1-Prevalence in controls) CIR= Prevalence in contacts/(1-Prevalence in contacts) A low CIR therefore suggests mainly household spread of infection, whereas a high value suggests frequent transmission outside the household . The adjusted CIR (for age, sex, sputum smear, nutritional status and household size) was 1.4 (95% Cl ; 0.70 - 2.37) compared with values of 0.18 - 0.40 in other studies (2) . Currently recommended tuberculosis control strategies are suitable for areas with low CIR. Different strategies may be needed for areas such as ours, with high values.