St. Louis Encephalitis

Reportable by Laboratories and Providers

About this Reportable Disease

Infectious agent: St. Louis Encephalitis Virus, member of the family Flaviviridae, genus Flavivirus.

Description of illness: Most persons infected with SLEV have no apparent illness. Initial symptoms of those who become ill include fever, headache, nausea, vomiting, and tiredness. Severe neuroinvasive disease (often involving encephalitis, an inflammation of the brain) occurs more commonly in older adults. In rare cases, long-term disability or death can result. There is no specific treatment for SLEV infection; care is based on symptoms.

Laboratory Reporting for this Disease

Arboviral Panel (IgG and IgM Antibody Assay)

TEST NAME	Arboviral Panel
DISEASE(S)/DISORDER(S)	Eastern Equine Encephalitis Western Equine Encephalitis St. Louis Encephalitis California Encephalitis (LaCrosse)
ALTERNATIVE NAME(S)	None
METHODOLOGY	Focus Diagnostics' Arbovirus IFA IgM Focus Diagnostics' Arborvirus IFA IgG
SPECIAL INSTRUCTIONS	Send acute sample at time of collection; do not wait for convalescent sample to be drawn.
ORDERING INFORMATION	Lab Web Portal PTBMIS: Test Order Code: ARBOVRS Test Order Description: Arbovirus Panel

Specimen Requirements

Patient Preparation	Paired Serum Samples: - Acute: drawn at illness onset and - Convalescent: drawn 7 to 14 days later Note: Send acute sample at time of collection; do not wait for convalescent sample to be drawn.
Specimen Collection	Asepticallly collect whole blood in Red Top tube (no anticoaglulant).
Specimen Labeling	Specimen must be labeled with at least two unique patient identifiers and match accompanying test order.
Specimen Processing	Allow sample to clot at room temperature prior to centrifugation. Aseptically transfer serum to a sterile, plastic, screw-capped vial.
Specimen Storage and Preservation	Store serum at 2 - 8°C. If shipping is to be delayed for longer than five (5) days, the specimen should be frozen at (-20)°C or colder.
Specimen Transportation	Ship specimen at 2 - 8°C. If specimen has been frozen, ship on Dry Ice. Specimen must be placed in an individual biohazard bag with absorbent material and should be shipped to the laboratory on the day of collection. All infectious substance shipments must conform to U.S. Department of Transportation (DOT) Hazardous Materials Regulations (HMR 49 C.F.R. Parts 171-180).
Specimen Acceptability and Rejection	The following submissions will not be tested: - Specimens not properly identified with the patient's name and date of birth and matching the submission form. - Convalescent serum that is collected sooner than seven (7) days from the collection date of the acute sample.
Testing Location	Knoxville

Laboratory Reporting

Reporting requirements apply to all laboratories located within Tennessee, as well as laboratories outside of Tennessee that test residents of Tennessee, including laboratories located within healthcare facilities. Healthcare providers and laboratories in the same healthcare facility both have a duty to report. The type of organisms and analytes laboratories must report to TDH for 2026 are indicated, and there are several ways laboratories can report results to TDH.

Manually report results to TDH by faxing or mailing a completed PH-1600 form to your local health department, or faxing to the state health office at (615) 741-3857
Automatically submit results to TDH via electronic laboratory reporting (ELR), which automates the process of sharing data with TDH using interoperability standards.
- See the ELR Onboarding Handbook for details on the onboarding process, checklist, frequently asked questions, business rules, message format, and vocabulary.
- To initiate the ELR onboarding process with TDH, register in the Trading Partner Registration (TPR) system TPR provides documentation for Promoting Interoperability (PI) attestation and milestone letters to document onboarding progress. Contact MU.Health@tn.gov for assistance.
Submit online via NBS. NBS is TDH's reportable disease system. To request an NBS account for reporting Complete this user survey to request an NBS account for reporting.
Blood lead levels can be sent via fax ( (615) 741-3857), entered online, or reported using the instructions at this link.

Information about this Reportable Disease for Healthcare Providers

Clinical Summary

St. Louis encephalitis virus (SLEV) is a mosquito-borne flavivirus. Most infections are asymptomatic, but the disease can range from a febrile illness to neuroinvasive disease (meningitis/encephalitis), which occurs more often in older adults.
Consider SLEV in any patient with an acute febrile or neurologic illness and recent mosquito exposure, especially during mosquito season in areas with reported activity; evaluate for other causes of encephalitis/aseptic meningitis as clinically indicated.
Diagnosis is primarily serologic: test for SLEV-specific IgM in serum and/or CSF; confirm positive IgM with neutralizing antibody testing at a state public health lab or CDC. Molecular testing may be considered in immunocompromised patients.
There is no specific antiviral treatment; care is supportive (and includes management of neurologic complications when present).
SLEV is a reportable condition in Tennessee; coordinate testing and public health notification per TDH guidance.

Clinical Links & Info

Review the case definition | CDC

Access the case report form (2018) | TDH

Collecting laboratory samples | CDC

Healthcare Provider Reporting

Healthcare reporting requirements apply to all providers located within Tennessee, as well as providers whose patients reside in Tennessee.

Providers must report cases of all diseases and conditions listed through one of these methods:

• Mail or fax a completed PH-1600 form to your local health department or fax to the state health office at (615) 741-3857

• Send automatically via electronic case reporting (eCR). See this TDH webpage for more information on eCR, register at the Trader Partner Registration website, or contact MU.Health@tn.gov for assistance.

• Submit online via NBS. NBS is TDH's reportable disease system. To request an NBS account for reporting Complete this user survey to request an NBS account for reporting.

• Blood lead levels can be sent via fax ( (615) 741-3857), entered online, or reported using the instructions at this link.

Information about this Reportable Disease for the Public

What It Is

St. Louis encephalitis is an illness caused by the St. Louis encephalitis virus (SLEV), which spreads to people through the bite of an infected mosquito. Many people infected do not get sick.

Signs and Symptoms

Symptoms can include fever, headache, nausea, vomiting, and tiredness. Severe illness can involve the brain (encephalitis) and may cause confusion or other neurologic symptoms.

How It Spreads

SLEV spreads through mosquito bites. It is not spread through casual person-to-person contact.

Diagnosis and Treatment

Healthcare providers diagnose SLEV using clinical evaluation and laboratory testing. There is no specific medicine to treat St. Louis encephalitis, so care focuses on relieving symptoms and supporting recovery.

Prevention

There is no vaccine for SLEV. Prevention focuses on avoiding mosquito bites (repellent, long sleeves/pants when possible, and reducing mosquito habitat around homes).

This Page Last Updated: March 25, 2026 at 8:53 PM