Tularemia (Francisella tularensis)
2026 Case Definition

Background

Tularemia is a zoonotic disease caused by the gram-negative coccobacillus Francisella tularensis. The bacterium is broadly distributed in the environment, including in water, hundreds of animal species, and some arthropods. Human infection occurs through several routes: tick or deerfly bites, contact with infected animal tissues, consumption of contaminated food or water, or inhalation. The source of human infection is sometimes unclear. Occupational exposures might occur, particularly in outdoor, veterinary, wildlife biology, or laboratory settings. Tularemia is not known to spread from person to person except in very rare circumstances. Tularemia characteristically presents as a febrile illness with various anatomically localizing signs or symptoms, depending on the route of infection. Severity of illness depends on route of infection, dose, and infecting strain; if not promptly treated with appropriate antibiotics, tularemia can be fatal.

Clinical Criteria

In the absence of another more likely etiology, a person with any of the following clinical manifestations, often accompanied by fever:

• Regional lymphadenopathy in absence of cutaneous ulcer (glandular tularemia), OR
• Regional lymphadenopathy with cutaneous ulcer (ulceroglandular tularemia), OR
• Conjunctivitis AND lymphadenopathy in the head or neck (oculoglandular tularemia), OR
• Cervical lymphadenopathy AND pharyngitis, tonsilitis, or stomatitis (oropharyngeal tularemia), OR
• Pulmonary disease such as pleural effusion, hilar adenopathy, pulmonary nodule, or pneumonia (pneumonic tularemia), OR
• Acute illness lacking localized signs and symptoms, characterized by fever (subjective or objective) AND one or more non-specific symptoms such as headache, myalgia, fatigue/malaise, or gastrointestinal illness (typhoidal tularemia), OR
• Other rare clinical manifestation(s) known to be associated with tularemia such as meningitis, septic arthritis, or endocarditis.

Laboratory Criteria

Confirmatory Laboratory Evidence: 

• Culture and identification of F. tularensis confirmed by a Laboratory Response Network (LRN) laboratory, OR
• Fourfold or greater change in serum antibody titer between acute and convalescent specimens^* , OR
• Change from a negative immunoglobulin G (IgG) AND a negative immunoglobulin M (IgM) serologic test result to F. tularensis antigen on an acute specimen to either a positive (IgG), a positive IgM, or both on a convalescent specimen. ^{*, †, ‡}

Presumptive Laboratory Evidence: 

• Detection of F. tularensis DNA directly from a clinical or autopsy specimen by molecular testing (e.g., polymerase chain reaction (PCR) or sequencing assay), OR
• Demonstration of F. tularensis antigen in tissue (e.g., by immunohistochemical staining).

Supportive Laboratory Evidence: 

• Positive IgG and/or IgM serologic test detecting antibodies to F. tularensis antigen (without documented fourfold or greater change or without prior negative result) in a patient with no history of tularemia vaccination.^†

Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.

^* To ensure consistency in laboratory methodologies, it is recommended that testing of paired sera for the purposes of confirmatory classification be conducted within the same laboratory. It is recommended that paired sera are collected 2-4 weeks apart but can be collected outside the range if clinically compatible or epidemiologic evidence is highly suggestive of tularemia.

^† For surveillance purposes, a borderline or equivocal serologic result is not considered as positive or negative.

^‡ A change from both negative IgG and IgM to positive results for both IgG and IgM is the strongest serologic evidence of tularemia infection; however, change to a positive result for only IgG or IgM may still indicate a true case of tularemia.

Epidemiologic Linkage

Within 21 days of illness onset or, when clinical information is not available, within 21 days of specimen collection:

Tier 1

• Known contact (including potential aerosol exposure) with an animal with direct laboratory detection or isolation of F. tularensis, OR
• Known handling of an F. tularensis isolate in a laboratory setting,

Tier 2

• History of a known or suspected tick or deerfly bite, OR
• Contact with an animal suspected to have tularemia (e.g., hunting or veterinary care), OR
• Activities with potential for aerosol-generating exposure (e.g., landscaping, mowing, or high-pressure spraying), OR
• Consumption of material potentially contaminated with F. tularensis, OR
• Shared exposure with another confirmed or probable tularemia case (i.e., part of a cluster), OR
• Other activities in occupational or recreational settings that could be linked to F. tularensis exposure.

Criteria to Distinguish a New Case from an Existing Case

• A person with a previously reported confirmed or probable case of tularemia may be enumerated as a new case when there is evidence of new clinically compatible acute illness after completing treatment for previous infection AND new laboratory evidence. As duration of antibodies to F. tularensis is not known, a person with persistently positive serologic tests in absence of new clinical or epidemiologic linkage criteria should not be enumerated as a new case

Suspect

• Meets confirmatory laboratory evidence OR presumptive laboratory evidence OR supportive laboratory evidence, OR
• Meets clinical criteria AND meets Tier 2 epidemiologic linkage evidence, OR
• Meets vital records criteria: death certificate lists tularemia as a cause of death or a significant condition contributing to death.

Probable

• Meets presumptive laboratory evidence AND meets clinical criteria, OR
• Meets presumptive laboratory evidence AND meets Tier 1 or Tier 2 epidemiologic linkage criteria, OR
• Meets supportive laboratory evidence AND meets clinical criteria AND meets Tier 2 epidemiologic linkage criteria, OR
• Meets supportive laboratory evidence AND meets Tier 1 epidemiologic linkage criteria, OR
• Meets clinical criteria AND meets Tier 1 epidemiologic linkage criteria.

Confirmed

• Meets confirmatory laboratory evidence AND meets clinical criteria, OR
• Meets confirmatory laboratory evidence AND meets Tier 1 or Tier 2 epidemiologic linkage criteria.

• Tularemia (Francisella tularensis) | 2017 Case Definition
• Tularemia (Francisella tularensis) | 1999 Case Definition
• Tularemia (Francisella tularensis) | 1996 Case Definition
• Tularemia (Francisella tularensis) | 1990 Case Definition