2022/2023 Influenza Season Data

The Pennsylvania Department of Health monitors influenza activity, conducts laboratory testing and compiles reports on flu activity throughout the year but ramps up surveillance activities in the fall and winter. The official influenza surveillance season starts with the 40th week of the year (typically around the beginning of October) and ends on the 20th week of the following year (in May). For the 2022-2023 season, the influenza surveillance season will begin on Oct. 10, 2022, and will run through May 20, 2023. Updated influenza activity data will be posted on this web page every Wednesday throughout the influenza surveillance season, beginning on October 12. 

These updates will provide a summary on:

1. When and where influenza activity is occurring;
2. Current trends in influenza as compared to previous seasons; and
3. What types and subtypes of influenza viruses are currently circulating. 

It is important to note that the influenza case counts presented on this page are restricted to only those cases that have had a positive laboratory test for flu (by rapid test, DFA, PCR or culture) reported to the PADOH. These case counts represent only a fraction of the actual burden of illness due to influenza occurring in the commonwealth at any given time. This is because most persons with influenza do not go to the doctor or are not tested or reported. Influenza spread and severity varies widely from season to season. It is estimated that five to 20 percent (600,000 to 2,400,000) of Pennsylvanians get the flu each year, and 120 to 2,000 die from complications of influenza.

Week 12 (Ending 3/25/2023)

Pennsylvania Weekly Influenza Report
Summary:

• Seasonal influenza activity in Pennsylvania and the United States is low.
  
• Flu activity decreased during the past few weeks; however, it is too soon to confirm if this will the end of flu season as activity might increase to create another wave similar to previous seasons.
  
• Influenza A and B are identified by laboratory testing; however, influenza A is the predominant type.
• During this flu season, influenza A(H3N2) viruses have been reported by the public health laboratory for most of the specimens that tested positive for flu.
  
• A total of 183,776 laboratory-confirmed influenza cases have been reported season to date. Confirmed reports were received from the 67 state counties.
  
• The percent of emergency department visits associated with influenza-like illness is moderate at this time.
  
• A total of 156 confirmed influenza-associated deaths have been reported during the current season.
  

Confirmed Influenza Laboratory Tests Received by PA DOH Surveillance

Table 1. Influenza Cases (positive by rapid test, PCR, or culture) Reported in Pennsylvania, 10/02/2022 to 3/25/2023 (n=183,766) - Cases by County and Influenza Type*¥

(*) Numbers smaller than 5 have been replaced with an asterisk

(¥) Influenza counts are provisional and may change as more information is received

(**) Test results may identify influenza Type A, influenza Type B, or influenza without specifying Type A or B. Some tests only give a positive or negative result and can-not identify influenza type.

Figure 1. Number of Pa. Influenza Cases by Week of First Report

Figure 2: Comparison of PA-NEDSS Influenza Cases (All Types) in Current Season to the Eight Previous Seasons

Figure 3: Season-to-date Influenza Sub-Typing Results From State Public Health Lab

Table 2: Season-To-Date Influenza-Associated Deaths by Age

Syndromic Surveillance

The Pennsylvania Department of Health's syndromic surveillance system receives data on visits to emergency departments (EDs) from most hospitals in the state.  The system looks at the reason for visiting the ED and determines if ED visits were likely due to influenza-like illness (ILI). The graph displays ED visits due to ILI as a percentage of total ED visits. This provides yet another way for the Department of Health to monitor influenza and ILI in the state. 

Figure 4: season-to-date Influenza-Like Illness (ILI) Emergency Visits

Figure 5: season-to-date Influenza-Like Illness (ILI) Emergency Visits by community health districts 

World Health Organization (WHO) and National Respiratory & Enteric Virus Surveillance System (NREVSS) Collaborating Laboratories

Thirteen clinical virology laboratories in Pa. are WHO and/or NREVSS collaborating laboratories for influenza surveillance.

These labs report weekly the number of respiratory specimens tested and the number positive for influenza types A and B to CDC. Some labs also report the influenza A subtype (H1 or H3) and influenza B lineage (Victoria or Yamagata). Because denominator data is provided, the weekly percentage of specimens testing positive for influenza is calculated.

Figure 7: Influenza Test Results Reported to the National Respiratory and Enteric Virus Surveillance System (NREVSS) Select Pennsylvania Laboratories, Season to date