Well-quantified tuberculosis exposure is a reliable surrogate measure of tuberculosis infection.
METHODS
Cape Town, South Africa.


OBJECTIVE
To develop a standardized, reliable measure of household tuberculosis (TB) exposure that considers child-specific risk factors.


METHODS
We assessed TB exposure in 536 children. Children were considered Mycobacterium tuberculosis  infected if two of three tests of infection were positive. Principal component analysis identified a discrete set of components that collectively described exposure and contributed to a composite contact score. Logistic regression assessed the odds of having M. tuberculosis infection  given increasing contact score while controlling for age and past TB treatment.


RESULTS
Four components described 68% of data variance: 1) maternal TB and sleep proximity, 2) index case infectivity, 3) duration of exposure, and 4) exposure to multiple index cases. Components were derived  from 10 binary questions that contributed to a contact score (range 1-10, median 5, 25th-75th interquartile range [IQR] 4-7). Among children aged 3 months to 6 years with household exposure, the odds of being M. tuberculosis-infected increased by 74% (OR 1.74, 95%CI  1.42-2.12) with each 1-point increase in the contact score.


CONCLUSIONS
Well-quantified TB exposure is a good surrogate measure of M. tuberculosis infection in child household contacts in a high-burden setting, and could guide targeted preventive treatment in children at highest  risk of M. tuberculosis infection.
Section on Retrovirology and Global Health, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030, USA. anna.mandalakas@bcm.edu
A M
AM
Mandalakas
H L
HL
Kirchner
C
C
Lombard
G
G
Walzl
H M S
HM
Grewal
R P
RP
Gie
A C
AC
Hesseling
D000328:Adult; D000367:Age Factors; D000995:Antitubercular Agents / Q000008:administration & dosage; D016009:Chi-Square Distribution; D002648:Child; D002675:Child, Preschool; D003140:Communicable Disease Control / Q000379:methods; D016358:Contact Tracing; D004334:Drug Administration Schedule; D004781:Environmental Exposure; D005191:Family Characteristics; D005260:Female; D006798:Housing; D006801:Humans; D007223:Infant; D059425:Interferon-gamma Release Tests; D007538:Isoniazid / Q000008:administration & dosage; D016015:Logistic Models; D008297:Male; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D016017:Odds Ratio; D011237:Predictive Value of Tests; D025341:Principal Component Analysis; D013902:Radiography, Thoracic; D018570:Risk Assessment; D012307:Risk Factors; D013019:South Africa; D013183:Sputum / Q000382:microbiology*; D011795:Surveys and Questionnaires; D013997:Time Factors; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology / Q000635:transmission
D000995:Antitubercular Agents; D007538:Isoniazid