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NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

Clinical Description

Signs and symptoms are variable, but chills followed by fever and sweating constitute the classic malaria paroxysm. The diagnosis should be considered for any person who has been exposed to infection. Complications such as cerebral malaria may occur in Plasmodium falciparum infection. Asymptomatic parasitemia may occur among immune persons.

Laboratory Criteria For Diagnosis

Demonstration of malaria parasites in blood films

Case Classification


A person's first attack of laboratory-confirmed malaria that occurs in the United States, regardless of whether the person has experienced previous attacks of malaria while outside the country


A subsequent attack experienced by the same person but caused by a different Plasmodium species is counted as an additional case. A repeated attack experienced by the same person and caused by the same species in the United States is not considered an additional case.

Blood smears from doubtful cases should be referred to the National Malaria Repository, CDC, for confirmation of the diagnosis.

In addition, cases are classified according to the following World Health Organization categories:

  • Autochthonous:
    • Indigenous: malaria acquired by mosquito transmission in an area where malaria is a regular occurrence
    • Introduced: malaria acquired by mosquito transmission from an imported case in an area where malaria is not a regular occurrence
  • Imported: malaria acquired outside a specific area (the United States and its territories)
  • Induced: malaria acquired through artificial means (e.g., blood transfusion, common syringes, or malariotherapy)
  • Relapsing: renewed manifestation (of clinical symptoms and/or parasitemia) of malarial infection that is separated from previous manifestations of the same infection by an interval greater than any interval due to the normal periodicity of the paroxysms
  • Cryptic: an isolated case of malaria not associated with secondary cases, as determined by appropriate epidemiologic investigations

Related Case Definition(s)