One issue is the access of individuals and communities to health care in terms of financial, geographical or socio-cultural constraints. Applications of the public health system include the areas of maternal and child health, health services administration, emergency response, and prevention and control of infectious and chronic diseases. The population in question can be as small as a handful of people or as large as all the inhabitants of several continents . Public health has many sub-fields, but typically includes the interdisciplinary categories of epidemiology, biostatistics and health services. Environmental health, community health, behavioral health, and occupational health are also important areas of public health. From ancient times, Christian emphasis on practical charity gave rise to the development of systematic nursing and hospitals and the Catholic Church today remains the largest non-government provider of medical services in the world.
- Asthma is another respiratory illness that many workers are vulnerable to.