Risk factors for positive tuberculin skin test in Guinea-Bissau.
BACKGROUND
The tuberculin skin test is used for tracing of tuberculosis transmission and identifying individuals in need of prophylactic treatment.


METHODS
Using a case-control study design, we recruited 220 smear-positive tuberculosis cases and 223 randomly selected healthy community controls in Bissau, Guinea-Bissau, during 1999-2000. Tuberculin skin tests were performed on family members of cases and controls (n = 1059 and n = 921, respectively). Induration of 10 mm or greater was considered positive. Risk factors were calculated for children (<15 years) and adults separately in multivariate logistic regression analysis.


RESULTS
The prevalence of positive tuberculin skin test was 41% in case-contacts compared with 22% in control-contacts, resulting in a prevalence ratio of 1.48 (95% confidence interval = 1.37-1.60). Positive skin tests among case-contacts increased with age for children, as well as with proximity to a case during the night, for both children and adults. A Bacille Calmette Guerin scar increased the likelihood of having a positive tuberculin skin test for adults in case households, but not in other categories of contacts. Among control-contacts the prevalence of positive skin test was associated with older age in children, history of tuberculosis in the family, and a positive tuberculin skin test of the control person.


CONCLUSIONS
Risk factors for a positive tuberculin skin test among case- and control-contacts are closely related to tuberculosis exposure. Having a BCG scar did not increase the risk of positive skin test in unexposed individuals. Tuberculin skin testing remains a useful tool for diagnosing tuberculosis infection.
Gustafson
Per
P
Infectious Diseases Research Group, Department of Clinical Sciences, Malmö, Lund University, Sweden. per.gustafson@med.lu.se
Lisse
Ida
I
Gomes
Victor
V
Vieira
Cesaltina S
CS
Lienhardt
Christian
C
Nauclér
Anders
A
Jensen
Henrik
H
Aaby
Peter
P
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001500:BCG Vaccine / Q000276:immunology; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D005260:Female; D006169:Guinea-Bissau / Q000453:epidemiology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012111:Residence Characteristics; D012307:Risk Factors; D012737:Sex Factors; D012959:Socioeconomic Factors; D014374:Tuberculin Test / Q000706:statistics & numerical data*; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000453:epidemiology* / Q000208:ethnology
D001500:BCG Vaccine