First level
Refers to the first level of contact between individuals and families with the health system. Primary care providers may be doctors, nurse practitioners, or physician assistants. There are some primary care doctors as well: ob-gyns, geriatricians, and pediatricians. Primary health care serves the community; it includes care for mother and child. It includes family planning, immunization, prevention of locally endemic diseases, treatment of common diseases or injuries, provision of essential facilities, health education, provision of food and nutrition, and adequate supply of safe drinking water.

Second level
Refers to a second tier of health system, in which patients from primary health care are referred to specialists for treatment.

Third level
Refers to a third level of health system, in which specialized consultative care is provided, usually on referral from primary and secondary medical care. Specialized intensive care units, advanced diagnostic support services, and specialized medical personnel are key features of tertiary health care.

Adapted from Primary, secondary and tertiary health care. Arthapedia. Internet. Accessed on November 7, 2018.