Data Sources
Influenza A, B, and RSV activity and trend levels are new for the 2026-27 season. The activity levels are determined using methods adapted from CDC, similar to the ED activity levels. COVID-19’s activity levels are just the ED activity level and will never be different.
The trend is calculated using case data for influenza A, B, and RSV. For COVID-19, the trend is calculated using ED visits and voluntarily reported case data. It looks at the difference between the current week (Tuesday – Monday) compared to the previous two weeks. The difference is weighted and categorized into 5 levels: decreasing rapidly, decreasing, stable, increasing, and increasing rapidly.
The map and bar graph show the number of positive tests for influenza A, B, and RSV (a respiratory virus) reported in Pennsylvania. This information comes from three sources: electronic lab reports sent to the Pennsylvania National Electronic Disease Surveillance System, manual entry, or summarized reports from clinics.
About one-third of our flu and RSV information comes from summarized reports. The summarized data uses the county of the healthcare provider, not the patient's county. It's summarized by the type of virus and the week it was reported.
The rates calculated for the rate map are cases divided by county population, per 100,000 people. Population data are estimates for 2025. View the original source.
This map shows total cases from the start of each respiratory season to the most recent Saturday. Counties are put into four groups (quartiles) based on their case numbers and rates and calculated the lowest and highest numbers for each group. Quartiles are labelled as “Low”, “Moderate”, “High”, and “Very High.”
Counties with 1-4 cases are redacted. At the beginning and end of the seasons, data may be limited.
The table shows flu subtyping data from the public health lab. The public health lab can identify H1N1 and H3. We assume that flu A H3 is H3N2.
COVID-19 case data is not available on the dashboard. COVID-19 cases are voluntarily reported in most PA counties.
Data provided for the figures are positive PCR/Antigen influenza (all types) and RSV (all types) tests reported to PA-NEDSS via ELR, manual entry, or aggregate reporting. Cases are aggregated by week of respiratory season.
Week 1 of respiratory season is the first week of October, and week 52 is the last week of September. For example, week 1 of the 2025-2026 season is September 28-October 4, 2025. For seasons that include week 53, such as the 2025–26 and 2020-21 seasons, counts for weeks 52 and 53 were averaged to avoid interruptions in the trendline. This is reflected in the graphs for week 13 (MMWR week 52). This means the seasonal comparison chart may not align entirely with the Weekly summary cases line chart.
The Pennsylvania Department of Health (PADOH) receives daily emergency department (ED) visit data from all hospital EDs in the Commonwealth. Most hospital ED visits are received within 24 hours of the visit taking place. ED visit surveillance provides PADOH with a rapid way to monitor the health of Pennsylvanians.
The chart shows different types of ED visits made by Pennsylvania residents each week as a percent of all reported visits. Using percent corrects for changes in the number of total ED visits reported over time. The Resp Line shows the percent of all ED visits where the patient’s stated reason for the ED visit included one or more respiratory symptoms (cough, runny nose, sore throat, etc.). The other three lines show the percent of all ED visits with a healthcare provider diagnosis for influenza, COVID-19, or RSV.
Important limitations: Data shown are ED visits and not individual patients, as one patient may have multiple ED visits during the period. Chart data for previous weeks can change over time as hospitals send new or updated ED visit data. Categorizing ED visits into visit types involves searching the visit data to look for symptoms mentioned of diagnosis codes included. Errors can occur from issues like misspellings or missing information. ED visit diagnosis codes may be incomplete or delayed.
Currently, around 80% of all reported ED visits include one or more diagnostic codes available within a few days of the initial ED visit. Recent decreases in the percentage of ED visits with a diagnosis can be caused by reporting delays. Patients who visit an ED usually have more severe illness and may differ in other important ways from the general population.
Starting for the 25-26 season, activity levels will be displayed on the ED Monitoring tab and Cover Page. To do this, we identified baseline (low activity) weeks using PA laboratory data from the National Respiratory and Enteric Virus Surveillance System. Using the mean and standard deviation of % of respiratory ED visits during the baseline weeks, we calculated z-scores to standardize the data. Cut points were calculated for each condition using the first quartile of z-scores and reversed back to the % of visits. The reversed cut points were used to classify the % of respiratory visits in the reference period into 5 activity levels. These methods are adapted from the CDC.
NHSN Data are from the respiratory (influenza, RSV, and COVID-19) hospitalizations reported to the National Healthcare Safety Network (NHSN) and are downloaded from CDC's Respiratory Virus Response Dashboard. Data are current for the previous week and are updated by the CDC on Thursdays. New admissions are broken into adult and pediatric admissions. These are aggregated for the week of data submission. Data are limited to what the CDC provides publicly. NHSN | CDC
Data are from the National Center for Health Statistics Mortality Surveillance System. They gather data from state death certificates, counting any death listed with flu or COVID-19. The data are summarized by the week of death. Since it can take time for death certificates to be processed, recent weeks' death counts might be lower than the real count. Counts and percentages for past weeks may change.
Many settings are required to report outbreaks to the PA DOH under Ch. 27. The majority of respiratory outbreaks occur in long-term care facilities (LTCF), which include nursing homes, skilled nursing facilities, personal care homes, and assisted living facilities. The threshold for an outbreak in an LTCF is 2 cases, which means more outbreaks are likely to be reported.
Congregate settings include group homes, homeless shelters, jails, and more. Healthcare facilities include hospitals, outpatient health centers, and psychiatric institutions. Other settings would be anything not listed under the other categories. These are rare.
Wastewater treatment facilities collect samples of untreated wastewater for testing at the Pennsylvania Bureau of Laboratories (BOL or a partner laboratory. Laboratories measure concentrations of traces of genetic material and share the results with the PaWSS team. The wastewater viral activity level (WVAL)is a numerical metric created by the Centers for Disease Control and Prevention’s National Wastewater Surveillance System (CDC NWSS).
The formula is: WVAL = e^(# of standard deviations relative to the baseline). For each virus, higher WVALs may suggest more disease spreading in a community. WVAL is divided into five categories based on the numeric value: minimal, low, moderate, high, or very high. The WVAL values that represent each category are different for each virus and are determined by CDC NWSS. The categories represent the amount of virus present in wastewater compared to past data measured at that location. These categories may provide information about the amount of disease spreading in a community.
Importantly, while the WVAL calculations are based on methods developed by CDC NWSS, the WVALs calculated by PaWSS may differ slightly from CDC’s due to small variations in the methods used for calculations. Visit the Pennsylvania Wastewater Surveillance System (PaWSS) | Department of Health | Commonwealth of Pennsylvania for more information.