Background: Tuberculosis (TB) remains an important infectious disease in New Zealand (NZ) and globally, but risk factors for transmission are still poorly understood. This research aimed to identify whether household crowding contributes to TB transmission in NZ. Methods: This ecological study used TB surveillance and census data to calculate TB incidence rates by census area unit (CAU). Census data were used to determine CAU characteristics including proportion of household crowding (a bedroom deficit of one or more), proportion of population who are migrants born in high-TB-incidence countries, median household income, and deprivation level. A negative binomial regression model was used to estimate the association between TB incidence and household crowding. Results: The analysis included 1898 notified TB cases for the 2000–4 period. Univariate analysis showed TB incidence at the CAU level was associated with household crowding, for the total population and for all ethnic and age groups. After adjusting for the covariates of household income, existing TB burden, and proportion of migrants from high-TB-incidence countries, multivariate analysis showed statistically significant associations between TB incidence and household crowding. The incidence rate ratio (IRR) was 1.05 (95% CI 1.02 to 1.08) in the total population and 1.08 (95% CI 1.04 to 1.12) for NZ-born people <40 years. Conclusion: At the CAU level, TB incidence in NZ is associated with household crowding. An individual-based study (e.g. case–control) in recently infected cases (detected by molecular epidemiology techniques) is suggested to complement these findings. Reducing or eliminating household crowding could decrease TB incidence in NZ and globally.

Background: Acute rheumatic fever (ARF) and its sequelae, chronic rheumatic heart disease, remain important causes of morbidity and mortality worldwide, but there is little recent information about risk factors. The aim of this study was to examine the association between ARF and household crowding in New Zealand between 1996 and 2005. Methods: This ecologic study used hospitalization data and census data to calculate incidence rates by census area unit (CAU). Rates of ARF were examined in relation to individual factors (age, ethnicity) and area factors based on the CAU of home address (household crowding, New Zealand deprivation index, household income, and proportion of children aged 5–14 years). The multivariate relationship between ARF incidence and CAU-based variables was assessed using a zero-inflated negative binomial model. Results: This study included 1249 new cases of ARF between 1996 and 2005. At the univariate level, ARF rates were associated with household crowding across all age groups and ethnicities. ARF rates were significantly and positively related to household crowding after controlling for age, ethnicity, household income, and the density of children in the neighborhood. The incidence rate ratio was 1.065 (95% confidence interval, 1.052–1.079) for the total population. Conclusions: In New Zealand, ARF rates are associated with household crowding at the CAU level. This finding supports action to reduce household crowding to improve health and reduce health inequalities. Our conclusion could be further investigated using a case-control study.