Viral Hemorrhagic Fever (VHF)
2025 Case Definition

Background

Viral hemorrhagic fevers (VHFs) are a group of illnesses caused by several families of viruses, including filoviruses (orthoebolaviruses and orthomarburgviruses), Old World arenaviruses (Lassa and Lujo viruses), New World arenaviruses (i.e., Guanarito, Machupo, Junin, Sabia, and Chapare viruses), Rift Valley fever virus, and Crimean-Congo hemorrhagic fever virus.

The Council of State and Territorial Epidemiologists position statement 24-ID-12 made the following updates to the case definition:

1. Updates to the clinical criteria, laboratory criteria, epidemiologic linkage, case classification, and addition of vital records evidence.
2. Addition of VHF caused by Rift Valley fever virus to the VHFs considered to be nationally notifiable.
3. An appendix is included in the updated position statement that provides incubation periods, reservoirs, and vectors to support public health practitioners with case ascertainment.

Clinical Criteria

• Acute onset of one or more of the following clinical findings*:
  • Subjective OR measured fever ≥38°C/100.4°F
  • Headache
  • Muscle and/or joint pain
  • Weakness and fatigue
  • Cough/difficulty breathing
  • Pharyngitis
  • Loss of appetite
  • Chest pain
  • Skin rash
  • Red eyes
  • Abdominal pain
  • Vomiting
  • Diarrhea
  • Intractable hiccups
  • Encephalitis or other neurological manifestations
  • Unexplained bleeding or bruising not related to injury or menstruation
  • Acute hearing loss**

*This list of signs and symptoms is not exhaustive and may be nonspecific; no sign or symptom is pathognomonic for VHFs.

**Relevant for Lassa fever.

Laboratory Criteria

 Confirmatory Laboratory Evidence:

• Detection of VHF-specific^ nucleic acid in blood or other body fluids, blood products, or tissues using a diagnostic molecular test (e.g., NAAT, genome sequencing), OR
• Detection of VHF-specific^ IgM by ELISA, OR
• Detection of a four-fold rise in VHF-specific^ IgG titer from an acute sample to a convalescent sample, OR
• VHF^ viral isolation in cell culture for blood, blood products (e.g., serum), or tissues.

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.

^VHF refers to viral hemorrhagic fever caused by filoviruses (Orthoebolaviruses and Orthomarburgviruses), Old World arenaviruses (Lassa and Lujo viruses), New World arenaviruses (Guanarito, Machupo, Junin, Sabia, and Chapare viruses), or viruses in the Bunyaviridae family (Rift Valley fever virus, Crimean-Congo hemorrhagic fever virus).

Epidemiologic Linkage

Within the incubation period of the VHF any of the following:

• Contact with a person who had known or suspected^^ VHF or any object contaminated by their body fluids
  without use of or confidence in proper adherence to, or experiences a breach in, recommended infection
  prevention and control (IPC) precautions, including personal protective equipment (PPE) use,
  OR
• Handles specimens that contain or might contain replication competent VHF viruses without use of or confidence
  in proper adherence to, or experiences a breach in, recommended IPC precautions, including PPE use,
  OR
• Handles bats, rodents, or primates that are or may be infected with a VHF without use of or confidence in
  proper adherence to, or experiences a breach in, recommended IPC precautions, including PPE use,
  OR
• Exposure to body fluids (i.e., urine, saliva, sweat, vomit, breast milk, amniotic fluid, semen, aqueous humor,
  or cerebral spinal fluid) from a person who clinically recovered from a VHF without use of or confidence in proper adherence to, or experiences a breach in, recommended IPC precautions, including PPE use,
  OR
• Residence in or travel to a VHF endemic area or area with active transmission† [see Appendix 1 in CSTE Position Statement 24-ID-12] AND an experience with any of the following scenarios for potentially unrecognized VHF exposures:
  • Contact with someone who was sick or died;
  • Visiting or work in a healthcare facility;
  • Breach in PPE and/or IPC precautions;
  • Visiting a traditional healer;
  • Attend or participate in funerals or burials;
  • Contact with animals;
  • Consumption of or handling raw meat;
  • Tick or mosquito bite;
  • Spent time in a mine or cave;
  • Any other scenario for previously unrecognized VHF exposure as determined in consultation with subject matter experts at CDC.

Note: Epidemiologic linkage criteria may require public health/CDC consultation to address any uncertainties and determine VHF risk. Please contact the CDC Emergency Operations Center (EOC) by phone at (770) 488-7100.

^^ Exposure may have occurred outside the U.S.

† As defined by public health authorities.

Criteria to Distinguish a New Case from an Existing Case

A new case of VHF should be enumerated only if not previously counted as a case of VHF caused by the same virus, as determined by laboratory evidence.^‡

‡ Among the VHFs included in this CSTE position statement reinfection with the same virus species has not been documented. There is a theoretical possibility that a VHF survivor could be infected by a virus that causes one of the other VHFs included in this CSTE position statement (ex. Lassa fever, Crimean-Congo hemorrhagic fever, etc.).

Suspect

• Meets clinical criteria AND meets epidemiologic linkage evidence

OR

• Meets vital records evidence.***

***A person whose death certificate lists VHF or infection with a VHF-causing virus (Ebola, Lassa, Marburg, Lujo, Guanarito, Machupo, Junin, Sabia, Chapare, Rift Valley fever, or Crimean-Congo hemorrhagic fever viruses) as an underlying cause of death or a significant condition contributing to death.

Confirmed

• Meets confirmatory laboratory evidence.

• Viral Hemorrhagic Fever (VHF) | 2022 Case Definition
• Viral Hemorrhagic Fever (VHF) | 2011 Case Definition
• Viral Hemorrhagic Fever (VHF) | 2010 Case Definition