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 2017-2018 influenza season summary report in a printable format.

Click here to download the last weekly report of influenza activity (from Dec. 2, 2018 through Dec. 8, 2018) in a printable format.


Febrile/flu-like illnesses at emergency departments remained virtually level for week 49 as compared with the previous week. Similarly, four positive specimens were reported from our sentinel hospital laboratory surveillance for influenza A and B during the same time period among the 6 participating laboratories—the same as the previous week. There were 3 reports of severe influenza (Philadelphia resident, positive by rapid test, PCR or culture, and hospitalized for = 24 hrs.) during this time frame, of which all hospitalizations were due to influenza A. One influenza-associated death has been reported so far this season. There were no influenza outbreaks (= 1 case of laboratory confirmed influenza) reported in a long term care facility during week 49.

Febrile/Flu-like Illnesses 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 “local” influenza activity, which is defined by CDC as outbreaks of influenza or increases in influenza-like-illness and recent laboratory confirmed influenza in a single region of the state. According to PADOH, influenza activity is low in all regions of the state but has increased from the past few weeks. From 9/30/18 to 12/8/18, there have been 1,245 laboratory confirmed cases of influenza (positive by rapid test, PCR, or culture). The majority of influenza throughout the state has been identified as influenza A (1,058 reports, 85%). Three influenza related deaths have been reported so far this season.

United States

Influenza activity remained slightly elevated throughout the U.S. during week 49. Widespread activity was reported by three states (California, Georgia, & Massachusetts), while regional influenza activity was reported by ten states. Local activity was reported by 21 states and sporadic activity was reported by 16 states, DC, and Puerto Rico. The percentage of respiratory specimens that tested positive for influenza decreased slightly for reporting U.S. clinical laboratories. Specifically, 18,516 specimens were tested at US clinical laboratories, and 665 (3.6%) specimens tested positive for influenza. Of those positive, 613 (92.2%) specimens tested positive for influenza A and 52 (7.8%) specimens tested positive for influenza B. Among the 207 positive influenza specimens received by public health laboratories for confirmatory testing and subtyping during this week, 196 (94.7%) were influenza A and 11 (5.3%) were influenza B. Of the 183 influenza A specimens subtyped, 35 (19.1%) were subtyped as H3N2 and 148 (80.9%) were subtyped as A(H1N1)pmd09. Since September 30, 2018, CDC has antigenically characterized 166 influenza viruses [97 influenza A(H1N1)pdm09, 45 influenza A(H3N2), and 24 influenza B viruses] collected by U.S. laboratories. All influenza A viruses collected were antigenically similar to the cell-grown reference viruses representing the 2018-2019 Northern Hemisphere influenza vaccine viruses. Of the influenza B lineages, all of the Yamagata lineage viruses matched the vaccine strain however, antigenically distinct subclades have emerged for the Victoria lineage. All viruses tested since late May show susceptibility to oseltamivir, zanamivir, and peramivir. Six influenza-associated pediatric deaths have been identified nationally this season, one during week 49.

Updated: 12/14/2018