Field testing along a disease gradient: some geographical dimensions of tuberculosis in Puerto Rico

The spatial pattern of reported tuberculosis incidence in Puerto Rico is characterized by numerous high-low gradients among continguous municipios. Tuberculin testing of some 1500 subjects along one such gradient reveals that there is no difference in sensitivity and suggests that the gradients are artifacts of reporting. Correlative associations with tuberculin conversion were generally weak, except for age-dependency. Collected personal histories demonstrated that the web of familial and intergenerational relationships is a major force in perpetuating the disease. Concealment of infection, denial and poor compliance in chemotherapy regimens compound the difficulties of case-discovery and case-control. Interviews in a sample of twelve health centers confirmed that, without the presence of trained and assigned tuberculosis nurses, the health care providers' 'index of suspicion' for tuberculosis is generally low. Absence of a tuberculosis clinic virtually dictates serious under-reporting of incidence in that municipio. Despite the success of Puerto Rico's control program over past decades, a reservoir of tuberculosis persists. The level of endemicity is relatively low but unsatisfactory in the context of public health aspirations.