Surveillance Data

The City is monitoring both seasonal and novel H1N1 influenza activity during the 2009-2010 influenza season. Daily and weekly updates (posted every Friday) will track trends in influenza-like illness (ILI) and show which influenza viruses are currently circulating in the city.

Current findings include:

Overall influenza activity is increased over baseline in New York City, indicating citywide circulation of influenza, but is still far below the levels seen in May and June of 2009.
Hospitalizations and deaths due to influenza A (including the novel H1N1 subtype) are increasing slowly in NYC; numbers are still low.
H1N1 remains the predominant influenza subtype currently present in NYC. A small amount of influenza B is also present. Laboratory surveillance shows increased circulation of both influenza and respiratory syncytial virus (RSV) in NYC during the past several weeks.

Visits for Influenza-like Illness to NYC Emergency Departments

Date	Hospitals Reporting	Total ILI visits	Total ED visits
11/19/2009	50	378	11,084
11/18/2009	50	429	11,460
11/17/2009	50	419	11,631

Table 1. Visits for influenza-like illness to New York City emergency departments. See note below.

Daily Number of Visits for Influenza-like Illness (ILI) Syndrome to NYC Emergency Departments - All Ages
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Figure 1. Visits for influenza-like illness to New York City emergency departments in recent weeks. See note below.

Influenza-like Illness Visits to NYC Emergency Departments, by Age Group

Rate of Influenza-like Illness (ILI) Syndrome Visits to NYC Emergency Departments, by Age Group
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Figure 2 - Rates of influenza-like illness (ILI) visits to New York City emergency departments (ED) are shown for four different age categories. See note below.

Influenza-like Illness Visits to NYC Emergency Departments, by Borough

Daily Number of Visits for Influenza-like Illness (ILI) syndrome to NYC Emergency Departments by Borough
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Figure 3 - The number of influenza-like illness (ILI) visits to New York City emergency departments (ED) is shown for each borough in New York City. See note below.

Influenza-like Illness Admissions from the Emergency Department

Weekly Number of Influenza-Like Illness Hospital Admissions at NYC Emergency Departments, All Ages
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Figure 4 - The Health Department follows trends in influenza-related hospitalizations by tracking the number of patients who are admitted from the emergency department (ED) with influenza like illness (ILI). See note below.

NOTE: The Health Department tallies ILI visits from 50 hospitals that together account for 95% of annual ED visits in NYC. An ILI visit means that the patient reported fever with cough or sore throat, or used the word “flu” to describe either their symptoms or their reason for the visit (for example, if they requested influenza testing). Syndromic surveillance is based on the patient’s main complaint when seeking care in an ED and does not capture the cause of the illness. Other illnesses (such as strep throat or the common cold) can cause ILI so not all ILI cases are novel H1N1 or seasonal influenza. Also, some people with true influenza may be missed because they do not report “fever with cough or sore throat” or “flu” as their main complaint. However, generally speaking, the total number of ILI visits does tend to track along with influenza activity in the community. These data are therefore most useful for following trends over time.