Plague is transmitted to humans by fleas or by direct exposure to infected tissues or respiratory droplets; the disease is characterized by fever, chills, headache, malaise, prostration, and leukocytosis that manifests in one or more of the following principal clinical forms:

	Regional lymphadenitis (bubonic plague)
	Septicemia without an evident bubo (septicemic plague)
	Plague pneumonia, resulting from hematogenous spread in bubonic or septicemic cases (secondary pneumonic plague) or inhalation of infectious droplets (primary pneumonic plague)
	Pharyngitis and cervical lymphadenitis resulting from exposure to larger infectious droplets or ingestion of infected tissues (pharyngeal plague)

Laboratory criteria for diagnosis

Presumptive

	Elevated serum antibody titer(s) to Yersinia pestis fraction 1 (F1) antigen (without documented fourfold or greater change) in a patient with no history of plague vaccination or
	Detection of F1 antigen in a clinical specimen by fluorescent assay

Confirmatory

	Isolation of Y. pestis from a clinical specimen or
	Fourfold or greater change in serum antibody titer to Y. pestis F1 antigen

Case classification

Suspected: a clinically compatible case without presumptive or confirmatory laboratory results

Probable: a clinically compatible case with presumptive laboratory results

Confirmed: a clinically compatible case with confirmatory laboratory results