This is the Utah Department of Health and Human Services (DHHS) end-of-season influenza report for the 2023–2024 season. DHHS also publishes a weekly report during the active influenza season that combines data from many sources to give the most complete and up-to-date picture of influenza activity in Utah. This end-of-season report presents influenza data from all the weekly reports for the 2023–2024 season.
Influenza is a contagious respiratory illness caused by a virus that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness and can sometimes lead to death. Find more information on the CDC site for Influenza (Flu).
Report date: September 27, 2024
*Note: Influenza-associated pediatric deaths are cases of persons younger than 18 years of age who had “influenza” listed as a cause of death. Novel influenza A virus infections include all human infections with influenza A viruses that are different from currently circulating human seasonal influenza H1 and H3 viruses.
The graphs below show data reported by emergency departments (EDs) that submit syndromic surveillance data to the National Syndromic Surveillance Program (NSSP) at the CDC. Currently, 100% of Utah’s EDs submit data (49 total). These data reflect the 7-day average of both the total number of visits and the percentage of visits that match CDC’s national syndromic definitions for influenza. Since January 1, 2019, these definitions only consider the diagnosis discharge codes for influenza. These data are reported based on clinical symptoms and not on lab results, and are intended to provide indications of trends occurring throughout Utah. The numbers and percentages presented are based on the patient’s address of residence when they visit an ED. For example, if a Davis County resident visits a Salt Lake County ED, the count will be associated with the Davis County numbers.
Each week, we collect the total number of deaths reported in Utah and the number of deaths for which pneumonia, influenza (flu), or COVID-19 was listed as an underlying or contributing cause of death on their death certificate. Unlike an influenza-associated pediatric death, an influenza-associated deaths in an adult is not a reportable condition in Utah. Many influenza-related deaths occur 1 or 2 weeks after a person’s initial infection, either because the person develops a secondary bacterial co-infection (such as bacterial pneumonia) or because influenza can aggravate an existing chronic illness (such as congestive heart failure or chronic obstructive pulmonary disease). As a result, influenza is infrequently listed on death certificates of people who die from influenza-related complications. Therefore, we cannot accurately report the number of influenza-associated deaths in adults. Instead, we monitor pneumonia, influenza, and COVID-19 deaths combined as a way to estimate how severe respiratory disease is in the community. In the graphs below, P&I refers to pneumonia and influenza deaths combined.
Mortality percentage: The percentage of mortality attributed to COVID-19 includes only death certificates that list COVID-19 as a cause of death but not influenza. The percentage of mortality attributed to pneumonia and influenza (P&I) includes only death certificates that list pneumonia and/or influenza as a cause of death but not COVID-19. Thus, death certificates that list both influenza and COVID-19 as causes of death are only included in the percentage of mortality attributed to pneumonia, influenza, and COVID-19 (PIC). There may be a lag in mortality reporting due to the time it takes to investigate and complete death certificates.
The methodology used for this report was adapted from the CDC FluView model for Mortality Surveillance.
Influenza-associated hospitalization (IAH) is a reportable condition in Utah. People meet the case definition for influenza hospitalization if they are hospitalized for any length of time and have a positive influenza laboratory test within a specific time frame. More information about this definition can be found on the Seasonal Influenza Disease Plan. Utah public health gathers a variety of data on influenza hospitalizations, including clinical features, course of illness, risk and protective factors, and influenza type and subtype. The Salt Lake County Health Department (SLCoHD) also has a contract with the Respiratory Virus Hospitalization Surveillance Network (RESP-NET), and conducts more in-depth investigations on each IAH case in their jurisdiction. IAH data from the SLCoHD can be found here. Data from influenza hospitalizations allow public health officials in Utah to better understand the groups of people most severely affected by influenza and help guide prevention messages and interventions. Data collection for the 2023–2024 influenza season began on October 1, 2023.
The U.S. Outpatient Influenza-like Illness Surveillance Network
(ILINet) is a national system that conducts surveillance for
influenza-like illness (ILI) in outpatient healthcare facilities,
including emergency departments. For this system, ILI is defined as
fever (temperature of 100ºF or higher) and a cough and/or sore throat.
These data provide an indication of ILI circulating in the community.
Note: As of April 14, 2024, some facilities are in the
process of changing how they report ILI data, which may result in
missing ILI data for the following weeks. We are working with these
facilities to re-establish reporting as soon as possible.
The Utah National Electronic Disease Surveillance System (UT-NEDSS) maintains influenza testing results from hospital laboratories and the Utah Public Health Laboratory (UPHL). UPHL tests influenza specimens to determine influenza type and subtype. Some specimens are also sent to the Centers for Disease Control and Prevention for additional typing and characterization. The results below include positive influenza tests reported to the Utah Department of Health and Human Services from both hospitals and outpatient facilities.
| Weekly count | Weekly percentage | Count | Percentage | |
|---|---|---|---|---|
| Influenza A | 17 | 77.3% | 14687 | 58.9% |
| Influenza A seasonal H1 | 0 | 0.0% | 1040 | 7.1% |
| Influenza A seasonal H3 | 2 | 11.8% | 458 | 3.1% |
| Influenza A, unsubtyped | 15 | 88.2% | 13189 | 89.8% |
| Influenza B | 5 | 22.7% | 10207 | 41.0% |
Influenza A viruses can be typed into different strains. The most common subtypes of influenza A viruses found in people are influenza A (H1N1) and influenza A (H3N2) viruses. In the spring of 2009, a new influenza A (H1N1) virus emerged that caused severe illness in humans. This new virus was very different from the human influenza A (H1N1) viruses circulating at that time and caused the first influenza pandemic in more than 40 years. That virus (often called “2009 H1N1”) has now replaced the H1N1 virus that was previously circulating in humans. Some influenza tests are unable to differentiate between influenza A strains, so a number of positive influenza A results reported to DHHS are unsubtyped.
Percent positivity: The above data represent samples tested from 25 Utah emergency departments. Because these data only come from people who are tested for respiratory illnesses in emergency departments, they do not represent disease trends in the general population and should be used along with other data sources. To learn more, visit the CDC RESP-LENS dashboard.