Influenza Surveillance

The Department of Health has a number of ways of gathering data and a staff of epidemiologists that work with CDC guidance to determine flu activity levels. This includes gathering reports on the number of patients with influenza-like illness from a sample of sentinel physicians and collecting data from hospital emergency rooms in the state. We also employ the services of the State Health Laboratory to determine which particular strains of the flu are prevalent.

H1N1 Testing

Influenza A (H1N1) PCR testing at the state laboratory is restricted to the current surveillance populations:

• Suspected cases of influenza in hospitalized patients.
• Suspected cases of influenza related deaths.
• State appointed influenza sentinel network physicians (sample frequency and numbers as directed).
• Pregnant women.
• Institutional clusters/outbreaks of influenza when directed by epidemiology staff.
• Selected health care workers, and/or other populations determined on a case by case basis and in consultation with epidemiology staff.

Current Flu Activity

Influenza Activity Level Criteria

Activity Level	Influenza Like Illness Activity* / Outbreaks	Laboratory Findings
No activity	Low	No confirmed cases†
Sporadic	Not increased	Isolated confirmed cases
		Confirmed outbreak in one institution‡
Local	Increased Influenza Like Illness (ILI) in 1 region **	Increased ILI within the past 3 weeks
	Two or more confirmed institutional outbreaks in 1 region	Influenza in region of outbreaks; virus activity is no greater than sporadic in other regions within the past 3 weeks
Regional (doesn’t apply to states with ≤4 regions)	Increased Influenza Like Illness (ILI) and/or confirmed institutional outbreaks in more than 2 but less than half of the state's regions	Confirmed Influenza in the affected regions within the past 3 weeks
Widespread	Increased Influenza Like Illness (ILI) and/or confirmed institutional outbreaks in at least half of state's regions	Lab confirmed influenza in the state within past 3 weeks..

* Influenza Like Illness (ILI) activity can be assessed using a variety of data sources including sentinel providers, school/workplace absenteeism, and other syndromic surveillance systems.
† Lab confirmed case a 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 predicative value positive 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.
‡  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 activity is reported to the Division of Public Health Surveillance and Informatics, Epidemiology Program Office, CDC, via the National Electronic Telecommunications System for Surveillance (NETSS) via Secure Data Network (SDN).