The Philadelphia Department of Public Health (PDPH) Division of Disease Control conducts weekly influenza surveillance using chief complaints from Emergency Departments, influenza-like illness visit data, laboratory-based surveillance and institutional surveillance during flu season. The results of this surveillance are posted here every Friday in the season.

Click here for more information on Influenza, including how and when to report a case and other disease guidance.

Click here to download the last weekly report of influenza activity (from May 13, 2018 through May 19, 2018) in a printable format.


During week 20, febrile/flu-like illnesses at emergency departments increased for children, however overall remained at baseline levels. Sentinel hospital laboratory surveillance for influenza A and B demonstrated slight decreases for specimens positive for both virus types as the number of reports were in the single digits. There were 4 reports of severe influenza (Philadelphia resident, positive by rapid test, PCR or culture, and hospitalized for ≥ 24 hrs.) during this time frame, of which 3 (75%) were due to influenza A. There were no influenza associated deaths reported during week 20 and the total number of influenza associated deaths so far this season is 49, including one pediatric case. There were no influenza outbreaks (≥ 1 case of laboratory confirmed influenza) reported in a long term care facility during week 20.

Febrile/Flu-like Illinesses at Philadelphia Emergency Departments 2017-2018 Data Compared to 4 Year Historical Weekly Averages Laboratory-based Surveillance for Influenza A: Philadelphia, 2013/2014 through 2017/2018 Seasons
Laboratory-based Surveillance for Influenza A: Philadelphia, 2013/2014 through 2017/2018 Seasons


The Pennsylvania Department of Health (PADOH) has reported “sporadic” influenza activity, which is defined by CDC as small numbers of laboratory-confirmed influenza cases or a single laboratory-confirmed influenza outbreak has been reported, but there is no increase in cases of ILI. Laboratory, hospital emergency department, and sentinel medical provider data indicate flu activity continues to decrease. The overall influenza activity has peaked at week 6 (week ending 2/10/2018). From 10/1/17 to 5/12/18, there have been 121,088 reports of influenza (positive by rapid test, PCR, or culture). The majority of influenza throughout the state has been identified as influenza A (79,611 reports, 65.7%). There have been 256 influenza related deaths reported this season, including seven pediatric deaths. PADOH no longer provided updated influenza data as of May 12, 2018, as flu activity decreased to baseline levels.

United States

Influenza activity continued to decrease in the U.S. during week 20. Widespread activity was reported in one state (CT), while one state (UT), Puerto Rico and Guam reported regional activity. Local activity was reported by seven states and sporadic activity was reported by the District of Columbia and 37 states. Four states reported no influenza activity. The percentage of respiratory specimens that tested positive for influenza continued to decrease during week 20. Specifically, 8,426 specimens were tested at US clinical laboratories, and 186 (2.2%) specimens tested positive for influenza. Of those positive, 85 (45.7%) specimens tested positive for influenza A and 101 (54.3%) specimens tested positive for influenza B. Among the 18 positive influenza specimens received by public health laboratories for confirmatory testing and subtyping, 6 (33.3%) were influenza A and 12 (66.7%) were influenza B. During October 1, 2017-May 19, 2018, CDC has antigenically or genetically characterized 3,263 influenza viruses [810 influenza A(H1N1)pdm09, 1,295 influenza A(H3N2), and 1,158 influenza B viruses] collected by U.S. laboratories. The majority of influenza A viruses collected were antigenically similar to the cell-grown reference viruses representing the 2017-2018 Northern Hemisphere influenza vaccine viruses, although some genetic diversity exists for the H3N2 viruses. In a smaller sample tested, the majority of influenza B viruses were antigenically similar to the vaccine strain, although a majority (78.2%) of the influenza B Victoria viruses contained a 6-nucleotide deletion. Sporadic instances of oseltamivir resistant and peramivir resistant influenza A(H1N1)pdm09 has been identified. A total of 169 influenza-associated pediatric deaths have been identified nationally this season, one during week 20. Two novel infections of influenza A (1 H3N2v and 1 H1N1v) were identified this season in persons who reported direct contact with swine. No human to human transmission has been identified.

Updated: 05/29/2018