Influenza (Flu) Surveillance

Current State Influenza Season Surveillance Reports


Previous State Influenza Season Surveillance Reports


Other Influenza Data

Influenza-associated pediatric mortality
Pandemic Data (archive)
U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet)

Surveillance Key Points

The state of Texas participates in influenza surveillance by reporting the estimated level of influenza activity to the CDC every week during influenza season (October to May). Influenza activity levels are reported as no activity, sporadic, local, regional, or widespread based on the definitions below.

There are 11 Health Service Regions in Texas. The Infectious Disease Control Unit (IDCU) of the Texas Department of State Health Services (DSHS), in cooperation with the DSHS Medical Virology Laboratory, monitors influenza around the state. Each season, local and regional health departments recruit providers throughout Texas to participate in laboratory surveillance. Health care providers at participating sites collect and submit specimens from patients with influenza symptoms to the DSHS lab on a weekly basis during influenza season.

Another portion of surveillance involves the CDC-sponsored U.S. Outpatient Influenza-Like Illness Surveillance Network (ILINet). Texas ILINet has 160 enrolled providers who voluntarily report outpatient influenza-like illness by age group to the CDC on a weekly basis; some providers also submit influenza surveillance specimens to the DSHS lab. Other laboratories, regional and local health departments, facilities participating in influenza research, and private physicians around the state also participate in influenza surveillance. It is through the efforts of health care providers and laboratories in Texas and all other states that the CDC develops a national picture of influenza virus activity, the geographic distribution of influenza viruses, and the clinical impact of the circulating viruses.

Influenza Activity Levels

No Activity Overall clinical activity remains low and there are no lab confirmed cases †


Isolated cases of lab confirmed influenza in the state; Influenza-Like-Illness* (ILI) activity is not increased.


A lab confirmed outbreak in a single institution‡ in the state; ILI activity is not increased.


Increased ILI within a single region** AND recent (within the past 3 weeks) laboratory evidence of influenza in that region. ILI activity in other regions is not increased.


Two or more institutional outbreaks (ILI or lab confirmed) within a single region AND recent (within the past 3 weeks) lab confirmed influenza in that region. Other regions do not have increased ILI and virus activity is no greater than sporadic in those regions.

(This level of activity does not apply for small states with 4 or fewer regions.)

Increased ILI in ≥2 but less than half of the regions AND recent (within the past 3 weeks) lab confirmed influenza in the affected regions.


Institutional outbreaks (ILI or lab confirmed) in ≥ 2 and less than half of the regions AND recent lab confirmed influenza in the affected regions.


Increased ILI and/or institutional outbreaks (ILI or lab confirmed) in at least half of the regions AND recent (within the past 3 weeks) lab confirmed influenza in the state.

† Lab confirmed case = case confirmed by rapid diagnostic test, antigen detection, culture, or PCR. Care should be given when relying on results of point of care rapid diagnostic test kits during times when influenza is not circulating widely. The sensitivity and specificity of these tests vary and the positive predictive value may be low outside the time of peak influenza activity. Therefore, a state may wish to obtain laboratory confirmation of influenza by testing methods other than point of care rapid tests for reporting the first laboratory confirmed case of influenza of the season. During periods of elevated influenza activity, the positive predictive value of rapid point of care tests will be higher.

* Influenza-Like-Illness (ILI) activity can be assessed using a variety of data sources including surveillance providers, school/workplace absenteeism, and other syndromic surveillance systems that monitor influenza-like illness.

‡ Institution includes nursing home, hospital, prison, school, etc.

**Region: population under surveillance in a defined geographical subdivision of a state. A region could be comprised of 1 or more counties and would be based on each state's specific circumstances. Depending on the size of the state, the number of regions could range from 2 to approximately 12. The definition of regions would be left to the state but existing state health districts could be used in many states. Allowing states to define regions would avoid somewhat arbitrary county lines and allow states to make divisions that make sense based on geographic population clusters. Focusing on regions larger than counties would also improve the likelihood that data needed for estimating activity would be available.

Influenza surveillance questions may be directed to Emilio Gonzales, Influenza Surveillance Coordinator.

Questions about the U.S. Outpatient Influenza-Like Illness Surveillance Network (ILINet) may also be directed to Emilio Gonzales.