Case definitions of priority diseases

A case definition is a set of standard criteria used to help you to separate true cases (those with the disease) from suspected cases that do not have the disease. Health professionals in higher health facilities and hospitals should use standard case definitions for reporting suspected priority diseases, i.e. a definition that has been agreed and should be used by all health professionals at higher levels within the country. Standard case definitions should be applied in the same way to all the persons examined.

Standard case definitions classify cases as confirmed or suspected. A confirmed case shows all the typical symptoms of a disease and the infectious agent or other cause has been positively identified in a laboratory investigation. For example, in a confirmed case of malaria, the patient shows symptoms typical of malaria, such as fever, headache and joint pain, the rapid diagnostic test (RDT) is positive, and laboratory investigation of a blood smear has confirmed that the person is infected with the Plasmodium parasites that cause malaria (figure below). On the other hand, a suspected case of malaria means that the person shows symptoms of malaria, but a laboratory investigation either has not been conducted yet, or has failed to find evidence of the parasite that causes malaria.

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Developmental stages of the malaria parasite (Plasmodium species); laboratory tests demonstrating these parasites in a patient's blood confirms a case of malaria.

A community case definition is a simplified version of the standard case definition, adapted to suit the needs and resources of primary healthcare professionals, community health volunteers, community members, traditional healers and birth attendants. It is useful to make a poster showing these definitionsl in the local language. The table below summarises an example of community case definitions for priority diseases.

Simplified community case definitions for use in identifying and reporting suspected priority diseases during community surveillance.

Priority diseaseSimplified community case definition
Acute watery diarrhoea in children aged under 5 years Any child having loose stools within the last 24 hours, or showing danger signs of loss of fluid from the body (dehydration)
Cholera Any person aged 5 years or older with lots of acute watery diarrhoea
Diarrhoea with blood and mucus Any person with diarrhoea and visible blood and mucus in the stools
Epidemic typhus Any person with sudden onset of headache and fever with chills, and general muscle pains, with or without spots (rash)
Guineaworm Any person with a history of emergence of worms from the leg
Leprosy Any person with loss of sensation and/or weakness in the muscles of the hands, feet or face; or loss of part of the hands or feet
Malaria Any person with fever, or fever with headache, back pain, chills, sweats, muscle pain, nausea and vomiting
Measles Any person with fever and spots (rash)
Meningitis Any person with fever and neck stiffness
Neonatal tetanus Any newborn who is normal at birth, but after two days becomes unable to suck or feed
Polio Any acute paralytic disease
Plague Any person with painful swelling(s) under the arms or in the groin area; in an area where plague is endemic, any person with a cough, chest pain and fever
Pneumonia Any child less than 5 years of age with a cough and fast breathing, or difficulty in breathing
Relapsing fever Any person with a fever that returns following a previous fever
Tuberculosis Any person with a cough lasting three or more weeks
Typhoid fever Any person with fever, constipation or diarrhoea, confusion (delirium) and with the body in a passively prone position (prostration)
Viral haemorrhagic fever Any person who has an unexplained illness with fever and bleeding, or who died after an unexplained severe illness with fever and bleeding
Yellow fever Any person with fever and yellowing in the white part of the eyes, or yellowing of the skin

You need to teach the community about these community case definitions of common diseases (figure below). The community can recognise and report common diseases to you if they understand these case definitions. The advantage of using community case definitions (instead of standard case definitions) is not only that they are simpler to understand. They are also 'broader' than standard case definitions, which means that more suspected cases will be identified using the community case definition, and fewer cases will be missed.

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A health professional teaching mothers the community case definition of malnutrition in children. Malnutrition is a weekly reportable condition. Simple definitions of immediately reportable diseases can also be taught in meetings like these. (Photo: UNICEF/Indrias Getachew)
Last modified: Wednesday, 9 July 2014, 3:22 PM