Session: Poster Session: Resistance in Mycobacteria
Monday, October 27, 2008: 12:00 AM
Room: Hall C
Background: Drug-resistant tuberculosis (TB) is spreading in global settings. Isoniazid is a first-line drug for TB prevention and treatment. We assessed the magnitude and characteristics of isoniazid-monoresistant (INHr) TB transmission in California (CA). Methods: For 2005-2007, we reviewed demographic data for INHr TB cases from the CA Registry of Verified Reports of Cases of TB, and spoligotype and mycobacterial interspersed repeat units (MIRU) data from the CA Universal Genotyping Project. We defined an INHr TB cluster as >2 cases with identical spoligotype and MIRU. We performed bivariate analysis of demographic characteristics of clustered and unclustered patients. We investigated a cluster among US-born patients (USB) by reviewing CA public health records and IS6110 restriction fragment length polymorphism (RFLP) surveillance data. Results: During 2005-2007, 342 INHr TB cases were identified; 294 (86%) were among foreign-born patients (FB). Of 194 (57%) cases with a genotype result, 74 (38%) were clustered and 120 (62%) were not. The 19 clusters included 2-20 cases; 16 involved >1 jurisdiction, 7 included USB, and one included a patient aged <5 years. Clustering was associated with USB (OR, 2.5; 95% CI, 1.1-5.9) and, among FB, with having lived >10 years in the US (OR, 2.3; 95% CI, 1.1-4.6). One cluster included 3 epidemiologically linked USB during the study period and was linked by RFLP to 4 USB from an outbreak in the 1990s. Conclusions: These molecular and demographic data, in conjunction with a confirmed outbreak and pediatric case, indicate that although the majority of INHr TB cases in CA result from immigration of infected persons, local transmission occurs and might be more frequent among USB and among FB who have lived >10 years in the US. To interrupt INHr TB spread, prevention efforts should target populations at highest risk for recent transmission.