Community infection ratio as an indicator for tuberculosis control.
The epidemiology of tuberculosis remains poorly understood. We investigated the relative importance of within-household and community transmission of infection among children aged 6 months to 14 years living in a Peruvian shanty-town. The prevalence of Mycobacterium tuberculosis exposure among 175 contact children (sharing a household with a person who had confirmed pulmonary tuberculosis) and 382 control children (living in nearby households free of active tuberculosis) was defined as the proportion of children with a positive purified protein derivative (PPD) skin-test. 97 (55%) contact children and 129 (34%) controls were PPD positive. Living in a contact household (odds ratio 1.74, 95% CI 1.11-2.73) and age (1.11, 1.06-1.18) were significant risk factors for PPD positivity. We calculated the community infection ratio (CIR) as the odds ratio of PPD-positive controls to PPD-positive contacts: CIR = [formula: see text] A low CIR therefore suggests mainly household spread of infection, whereas a high value suggests frequent transmission outside the household. The adjusted odds ratio (for age, sex, within-household correlation, and household size) was 0.40 (95% CI 0.26-0.64), compared with values of 0.18-0.37 in studies elsewhere. Currently recommended tuberculosis control strategies are suitable for areas with low CIRs. Different strategies may be needed for areas, such as that we studied, with high values.
AB Prisma, Lima, Peru.
G
G
Madico
R H
RH
Gilman
W
W
Checkley
L
L
Cabrera
I
I
Kohlstadt
K
K
Kacena
J F
JF
Díaz
R
R
Black
D000293:Adolescent; D000367:Age Factors; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D003140:Communicable Disease Control / Q000191:economics; D017714:Community-Acquired Infections / Q000453:epidemiology; D016358:Contact Tracing; D003906:Developing Countries; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D016017:Odds Ratio; D010568:Peru / Q000453:epidemiology; D011204:Poverty Areas; D015995:Prevalence; D014397:Tuberculosis, Pulmonary / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D014504:Urban Health