Current Year Data (2026)

Key points

• ArboNET is a national arboviral surveillance system managed by CDC and state health departments.
• These data are preliminary and subject to change.
• Current season data are updated every one to two weeks during June through December.
• Due to delays in reporting, state, territorial, and local health departments may have more up-to-date information than what is presented here.

View the data for St. Louis encephalitis

Data are current as of September 22,** 2026.**

Limitations of ArboNET data

Surveillance data have several limitations that should be considered when using and interpreting the data.

• Under-reporting is a limitation common to all surveillance systems that rely on healthcare providers to consider the disease as a possible diagnosis in a patient, obtain the appropriate laboratory test, and report confirmed cases to public health authorities.
• Cases of mild illness (non-neuroinvasive disease) are more likely to be underreported compared to more severe disease (neuroinvasive) cases. The degree of underreporting varies by disease awareness and healthcare-seeking behavior in any area. Surveillance data for non-neuroinvasive disease should not be used to make comparisons of disease activity between different locations or over time.
• Surveillance data are reported by county of residence, not the location (county or state) of exposure.
• Non-human surveillance is conducted variably across the country. Absence of non-human activity reported to CDC should not be interpreted as no risk.
• There is a lag in case reporting to CDC and states and territories may publish surveillance data on different schedules than CDC

On This Page

• View the data for St. Louis encephalitis
• Limitations of ArboNET data

Sept. 22, 2026

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National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)About This Page

Published: May 15, 2024

Updated: September 22, 2026This page was last updated on this date. Updates may include minor edits, image changes, or other modifications to page content.

Reviewed: September 22, 2026The information on this page was last reviewed by subject matter experts to ensure accuracy.

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