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 Apr. 7, 2019 through Apr. 13, 2019) in a printable format.


Febrile/flu-like illnesses decreased for adults and children ages 0-4 years, but slightly rose for children and adolescents ages 5-17 years. The number of influenza positive specimens reported from our sentinel hospital laboratory surveillance network continued to decline, as 113 specimens were positive for flu A and only 5 were positive for flu B. There were 12 reports of severe influenza (Philadelphia resident, positive by rapid test, PCR or culture, and hospitalized for = 24 hrs.) during this time frame, of which 10(83.3%) were due to influenza A. Twenty-seven influenza-associated deaths have been reported so far this season, including two during week 15. There were no influenza outbreaks (= 1 case of laboratory confirmed influenza) reported in a long term care facility during week 15.

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 “regional” influenza activity, which is defined by CDC as outbreaks of influenza or increases in influenza-like-illness and recent laboratory confirmed influenza in at least two but less than half the regions in the state. According to PADOH, influenza activity has continued to decrease during the past week in all state regions, however activity is still higher than epidemic threshold. The highest influenza activity was reported in the northwest region. From 9/30/18 to 4/15/19, there have been 94,417 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 (90,588 reports, 95.9%). One hundred twenty-eight influenza-associated deaths have been reported so far this season, including two pediatric deaths.

United States

Influenza activity continued to decrease but remained elevated in the U.S. during week 15. Influenza A(H1N1)pdm09 viruses predominated from October to mid-February and Influenza A(H3N2) viruses have been more commonly identified since late February. Small numbers of influenza B viruses have also been reported. Widespread influenza activity was reported by 11 states, while regional activity was reported by Puerto Rico and 20 states. Local activity was reported by 17 states and DC and sporadic activity was reported by two states. The percentage of respiratory specimens that tested positive for influenza decreased for reporting U.S. clinical laboratories. Specifically, 22,526 specimens were tested at US clinical laboratories, and 2,669 (11.8%) specimens tested positive for influenza. Of those positive, 2,266 (84.9%) specimens tested positive for influenza A and 403 (15.1%) specimens tested positive for influenza B. Among the 353 positive influenza specimens received by public health laboratories for confirmatory testing and subtyping during this week, 321 (90.9%) were influenza A and 32 (9.1%) were influenza B. Of the 313 influenza A specimens subtyped, 77 (24.6%) were subtyped as A(H1N1)pmd09 and 236 (75.4%) were subtyped as A/H3N2. Since September 30, 2018, CDC has antigenically characterized 1,898 influenza viruses [950 influenza A(H1N1)pdm09, 703 influenza A(H3N2), and 245 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 2018-2019 Northern Hemisphere influenza vaccine viruses, although some genetic diversity exists for the H3N2 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. The majority of influenza viruses tested show susceptibility to oseltamivir and peramivir. All influenza viruses showed susceptibility to zanamirvir. Ninety-one influenza-associated pediatric deaths have been identified nationally this season, five during week 15.

Updated: 04/23/2019