Epidemiology of extrapulmonary tuberculosis, Alameda County, California, 2010-2021.

Background: Extrapulmonary tuberculosis (EPTB) represents a range of disease manifestations, and is a major contributor to ongoing TB burden in the United States. We examined the incidence, trends and characteristics of EPTB in a high-burden TB county in Northern California. Methods: We extracted surveillance data for all TB cases in Alameda County during 2010-2021. TB was classified per national surveillance definitions, and EPTB included any site involvement other than the lung. We determined overall and annual incidence of EPTB in comparison to pulmonary TB (PTB), and assessed trends in incidence using Poisson regression and proportion with Joinpoint regression. We further compared clinical and demographic characteristics by TB site of disease. Results: Of 1,336 TB cases included, 372 (28%) had EPTB disease only. Lymph nodes were the most common site (38.7%), followed by pleura (17.7%), peritoneal (5.4%), and bone (4.8%). From 2010 to 2021, EPTB incidence decreased by 52% from 3.5 to 1.7 cases per 100,000. However, the proportion of TB cases that were extrapulmonary increased from 2015 to 2021 (8.3% annual change, 95% CI 5.2%-14.2%). In comparison to PTB, EPTB case-patients were more likely to be aged < 45 years old, have end-stage renal disease, and pyrazinamide monoresistance, but less likely to have microbiological confirmation. Conclusions: EPTB incidence has decreased over time, but the proportion of EPTB cases increased. Greater awareness of clinical and demographic characteristics of EPTB may guide targeted interventions to support TB elimination.