Evaluation Of Mycobacterium Bovis Surveillance In California, 2000-2010

BACKGROUND:   Since 1993, the number of tuberculosis (TB) cases in California has steadily declined while the incidence of Mycobacterium bovis (M. bovis), part of the Mycobacterium tuberculosis complex, has remained unchanged. From 2000-2010, there were 850 M. bovis cases, which constituted 3.7% of all TB cases in California. To achieve the United States goal of TB elimination by 2035, targeted efforts for M. bovis are needed. Currently, the national tuberculosis surveillance system contains limited data on risk factors for M. bovis to aid in TB control efforts.

METHODS:   We evaluated the California Department of Public Health TB Control Branch’s (TBCB) and local TB health jurisdictions’ (LHJ) surveillance system’s ability to identify and investigate M. bovis cases using CDC’s Updated Guidelines for Evaluating Public Health Surveillance Systems. The sensitivity and positive predictive value of mono-pyrazinamide resistance (from TBCB’s surveillance system records) as a case definition for M. bovis was calculated using spoligotyping (from Tuberculosis Genotyping Information Management System) as the gold standard. Timeliness was evaluated by calculating the median number of weeks from TB suspect report date to the report date of mono-pyrazinamide resistance and spoligotyping. To assess acceptability, representativeness, and usefulness, LHJs that reported at least one M. bovis case from January 1, 2000 to December 31, 2010 completed a survey regarding data collection and interventions related to M. bovis.

RESULTS:   The mono-pyrazinamide resistance case definition had high sensitivity (93%) and positive predictive value (82%). The median time from the TB suspect report date to report date of mono-pyrazinamide resistance and spoligotyping was 14 weeks and 24 weeks respectively. Of the 34 LHJs that received a survey, 20 (59%) responded; accounting for 93% (792/850) of the M. bovis cases occurring from 2000-2010. TBCB and 16 (80%) LHJs reported not collecting data regarding the route of transmission of M. bovis as part of their TB case intake. Fourteen (70%) LHJs reported that their case management did not change if a patient was identified with M. bovis versus M. tuberculosis. Fifteen (75%) LHJs stated the TBCB surveillance system should collect M. bovis risk factors.

CONCLUSIONS:   Mono-pyrazinamide resistance can be used as a surrogate measure of M. bovis. California’s surveillance systems can detect M. bovis cases but are limited in their ability to capture risk factors and transmission routes to help inform prevention efforts for M. bovis. To inform local and statewide interventions, capture of key risk elements should be considered.