Testing and Follow-up
All participants received Mantoux tuberculin skin testing with 0.1 mL of 5 Tuberculin Units of PPD applied on the volar aspect of the arm to produce a wheal of at least 6 mm. Patients were instructed to return in 48 hours for test results, except those tested on a Friday were asked to return in 72 hours. Patients who did not return in 48 hours were telephoned that day and asked to come in later in the day or by the next day (within 72 hours). Postcards were mailed to all nonadherent patients without telephones, instructing them to return for retesting. We maintained a log of the test date, patient's name, medical record number, telephone number, and test result(s).
Initial interpretation of PPD results was performed by trained nurses and documented in the logbook and medical record. Nurses were blinded to the results of the questionnaire. If a nurse detected an induration or was uncertain, a physician assessed the patient immediately. All positive results were confirmed by a physician and measured with a ruler calibrated in millimeters. Parental reports and self-assessment of results were not accepted.
Positive PPD skin test reactions were defined as indurations >10 mm, in accordance with the AAP's guidelines.10 Chest radiographs were obtained for all patients with positive results.
Statistical Analysis
Data were entered and analyzed using SPSS (Chicago, Ill). A "yes" response to any question was considered sufficient to warrant PPD testing. We determined the sensitivity (the probability that children with a positive PPD result would be targeted for screening), the specificity (the probability that children without a positive PPD result would not be targeted for screening), the positive predictive value (the probability of a positive PPD result among children targeted for screening), and the negative predictive value (the probability of children not targeted for screening having a negative PPD result) for each risk assessment question and for different combinations of the questions.
We calculated the prevalence of positive PPD results and reviewed the results of chest radiographic studies. To calculate odds ratios (ORs) and compare risk factors for TB, we classified the children on the basis of test results into a positive PPD group and a negative PPD group. We assessed differences in TB risk factors between these groups. Odds ratios for various combinations of risk factors for TB were calculated by univariate and multivariate analyses.
Subsequent Analysis
After initial analyses, children older than 11 years were found to account for 75% of those with a positive skin test result and no identifiable risk factor. Hence, we determined the sensitivity, specificity, positive and negative predictive values, and OR of age older than 11 years as a specific risk factor and in combination with the results of the NYCDOH questionnaire.