Influenza Activity

Information and resources on influenza activity in New Hampshire

Influenza is not a reportable disease in New Hampshire, but surveillance (data) systems are in place to help determine the reach of illness and current virus types being spread.

Weekly Influenza Activity Report

Timing: During the traditional influenza season (beginning of October through mid-May).

What data is included?

Data from heath care providers and laboratories
Data from other state and national surveillance systems.
NH influenza activity for the week.

New Hampshire participates in the US Outpatient Influenza-like Illness Surveillance Network (ILINet), a collaborative effort between the CDC, the NH Department of Health and Human Services, and health care providers throughout the State, and surveillance data reported by ILINet sentinel providers is included in the weekly reports.

Weekly Report

Upon conclusion of the traditional influenza season, surveillance data is summarized in the form of an annual season summary report.

Season Summary Report

This report summarizes:

The severity of the most recent influenza season, including
When influenza activity peaked based on different surveillance measures, such as:
- Acute respiratory illness,
- Number respiratory specimens that test positive for influenza (by influenza type), and
- The total number of influenza-related deaths.

Surveillance data are summarized to determine which age groups are most affected.

Data are compared to the previous influenza season and to regional and national surveillance data to help put the data into perspective.

In addition to surveillance data presented in the Season Summary Report, information on annual vaccination rates among healthcare personnel in hospitals, ambulatory surgical centers, and assisted living facilities can be viewed by visiting the Healthcare-Associated Infections Program.

Any suspect outbreak, cluster of illness, unusual occurrence of communicable disease, or other incident that may pose a threat to the public’s health must be reported within 24 hours of recognition. Any infections with novel or avian influenza, as well as pediatric influenza-related deaths, would be considered “implicitly” reportable.

Flu Season Summary Reports

NH Acute Respiratory Illness (ARI) Surveillance by County

Provided below are maps for each week during the regular influenza season, which begins in early October and continues through mid-May. The maps show intensity of Acute Respiratory Illness (ARI) for each of the ten New Hampshire counties.

2023-2024 Season

2022-2023 Season

The Influenza Surveillance Program monitors influenza activity in New Hampshire throughout the year. However, the weekly influenza surveillance reports are only completed and posted during the course of the regular influenza season, which spans from early October through mid-May the following year.

What data is included?

Key components for influenza surveillance are as follows:

Virologic Surveillance

Influenza test results are obtained and reported out on from two main sources, including NH Public Health Laboratories (NH PHL) and Hospital Clinical Laboratories.

NH Public Health Laboratories (NH PHL)

Results from specimens collected from patients in outpatient settings (such as hospitals and doctors’ offices) and institutional settings (such as long-term care facilities) that are submitted to the NH PHL for testing.

The NH PHL tests specimens using a method known as reverse transcription-polymerase chain reaction (RT-PCR) assay, which allows for determination of both influenza type (e.g., flu A or B) as well as influenza subtype (e.g., influenza A(H3) or A(H1N1)).

Hospital Clinical Laboratories

Weekly reports for flu results are submitted by Hospital Clinical Laboratories.

Summary of test results are transmitted to Bureau of Infectious Disease Control from participating hospital clinical laboratories across the state. These hospital clinical laboratories report:

The total number of specimens that are tested for flu each week, and
The number that test positive for either flu A or flu B.

All virologic surveillance data are summarized on a weekly basis throughout the year in the influenza surveillance reports that are published during the regular flu season (spans from early October through mid-May).

Outpatient Illness Surveillance

Outpatient Illness Surveillance is performed on a weekly basis throughout the year by looking at two different sources of data, including:

U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet)
ILINet is a collaborative effort between the CDC, the NH Department of Health and Human Services, and health care providers throughout the State. More information about ILINet can be found here. For this system, ILI is defined as fever (temperature of 100°F [37.8°C] or greater) and a cough and/or a sore throat.
Automated Hospital Emergency Department Data (AHEDD) system
The AHEDD system is a collaborative effort between NH acute care hospitals and the NH DHHS. Currently, 26 hospitals electronically transmit real-time data from emergency department encounters throughout the day to NH DHHS. Using a method known as syndromic surveillance, chief complaint text within the AHEDD system is queried for complaints of acute respiratory illness (ARI) in patients seen in emergency departments.

Mortality Surveillance

The percentage of all deaths that occur each week due to pneumonia and influenza (P&I) are assessed and reported out during the regular flu season in the weekly influenza surveillance report. Deaths due to P&I are identified through review of electronically filed death certificates by looking at the causes of death listed on each certificate. This data entails surveillance of all deaths recorded by NH’s Division of Vital Records Administration.

Each week during the regular season the number influenza-related deaths identified for the season to date are reported.