BRIEF REPORTS THE TRANSMISSION OF TUBERCULOSIS IN SCHOOLS INVOLVING CHILDREN 3 TO 11 YEARS OF AGE Jonathan R. Roberts, MPH, PhD, MFPH,* Brendan W. Mason, MSc, MB ChB,† Shantini Paranjothy, MSc, MB BCh, PhD,‡ and Stephen R. Palmer, MA, MB BChir, FRCP, FFPH‡ Abstract: Little is known about the risk of tuberculosis transmission from children. We reviewed the published literature on the transmission of tuberculosis during outbreaks involving children 3 to 11 years of age and report that transmission rates among close contacts in school outbreaks are on average higher (weighted average 69.8% vs. 39.3%) if the index case is a child than an adult. Key Words: tuberculosis, transmission, contact tracing, schools Accepted for publication August 16, 2011. From the *Public Health NHS Bristol, Bristol, United Kingdom; †Communi- cable Disease Surveillance Centre, Public Health Wales, Temple of Peace and Health, Cathays Park, Cardiff, United Kingdom; and ‡Department of Primary Care and Public Health, School of Medicine, Cardiff University, Cardiff, United Kingdom. The authors have no funding or conflicts of interest to disclose. Address for correspondence: Jonathan R. Roberts, MPH, PhD, MFPH, Public Health Directorate, NHS Bristol, 4th Floor South Plaza Building, Marl- borough Street, Bristol, BS1 3NX UK. E-mail: Jonathan.roberts2@nhs.net. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.pidj.com). Copyright © 2012 by Lippincott Williams & Wilkins DOI: 10.1097/INF.0b013e31823378c9 T ransmission of tuberculosis (TB) from children is thought to be rare, 1 although transmissions from very young children (age 12 weeks) have been documented. 2 In outbreak settings involving schools, transmission is reported to vary from 1 in 3 to 1 in 50 contacts, 3 which may be influenced by Bacillus Calmette-Gue ´rin (BCG) status, 4 the virulence of the organism, or degree of expo- sure to environmental factors such as second-hand smoke. 1,5,6 Studies looking at transmission to children where contact has occurred in a household setting (from an adult source) estimate transmission rates between 30% and 50% to close contacts 7 ; however, little is known on transmission from a child source or in settings outside the house. As tests to determine transmission have evolved and the interferon-gamma release assays (IGRAs) are now available for routine use, there are new opportunities to accurately study the transmission of TB which have not been possible due to limitations of the tuberculin skin test (TST) method, such as confounding with previous BCG, sensitivity, and the boosting effect of repeated tests. 8 Systems for capturing data on all TB diagnoses and contact tracing are often limited due to a lack of detail of contact screening method, case definitions, and low participation rates. 5,9,10 Pub- lished outbreak reports therefore represent an opportunity to study transmission in school settings where there are also likely to be additional pressures for information from public health officials from concerned parents, teachers, and the local media, in addition to multicultural needs and fear and anxiety. 11 In this article, we report a systematic analysis of published reports of outbreaks of TB in school settings to calculate trans- mission rates, with the aim of informing public health officials. MATERIALS AND METHODS We searched the following databases: Medline (1950 –Feb- ruary 2011), Embase (1960 –February 2011), CINHAL (1980 – February 2011). Search strategies were adapted for each database but limited to English language studies. Bibliographies of studies identified were checked for any additional references. Inclusion and Exclusion Criteria. We included studies that de- scribed screening contacts after an index case with TB (adult or child) had contact with children in a school setting. We defined close contacts as classroom contacts of the index case and wider contacts as children outside this group. Individual case studies, non-English language studies, and reports with limited detail were excluded. A full list of excluded studies can be obtained from the authors. Data Extraction. Data extraction was independently carried out by 2 reviewers. Data were collected on the type of setting (eg, nursery, nursery school, infant, or junior school), transmission rate, and factors associated with the transmission rates (including in- fection status of the incident case and strain of TB). Population characteristics including ethnicity, gender, and socioeconomic sta- tus were also recorded. Statistical Analysis. Transmission rates were summarized by cal- culating a weighted average and corresponding 95% confidence interval (CI). Studies were weighted by the number of contacts screened as transmission rate would be less precise if only a small number of contacts were screened. The weight of each study was calculated as the inverse of the variance for that study. The 95% CIs were calculated from the standard error (obtained from the variance) using standard statistical formula. Results are presented separately according to whether the index case was a child or adult. All transmission rates described relate to transmission to children. RESULTS Twenty-nine studies were identified after reviewing the titles and abstracts of the database searches. Twelve studies met the inclu- sion criteria. 6,12–22 Data flow of studies and data extracted from the studies are presented in the online supplementary materials (Table, Supplemental Digital Content 1, http://links.lww.com/INF/A951; Fig., Supplemental Digital Content 2, http://links.lww.com/INF/A952). Ten studies (83%) described the index cases smear status, but sociodemographic details were not always present. All studies gave details of the screening test used (Table 1). Confirmation of Transmission. In 2 studies, 6,19 the strain of TB was identified by DNA typing to confirm contacts were infected with the same clone as the index case. Four studies reported the baseline (expected) TST reactivity prevalence for the populations where the incident occurred. This information demonstrates that transmission is likely to have occurred from the source case and positive tests are not likely to be simply identification of previ- ously unidentified infection. In 3 studies, the baseline level of TST positives was below 2% in their respective populations, increasing to 13%, 42.5%, and 51% within the studies. 15,16,19 In the fourth study, 20 the baseline level was higher at 9.8% and increased to 15.8% within the study. Overall Rate of Transmission. The number of close contacts screened ranged from 24 to 43 and transmission rates varied between 9.8% and 69.8%. In wider contacts, the range was 29 to 722 and transmission rates varied between 2.9% and 72.4%. Transmission From a Child Index. Five studies 6,15,17,19,20 reported on an index case who was a child in the school. Three studies 6,17,19 reported screening close contacts of children and the number of contacts screened ranged from 24 to 43. The transmission rates varied between 66.7% and 72.4%. The weighted average transmission was 69.8% (95% CI: 60.7%–79%). Four studies 15,17,19,20 extended tracing The Pediatric Infectious Disease Journal • Volume 31, Number 1, January 2012 82 | www.pidj.com