Influenza is retreating in Wisconsin.
Across the U.S. there were 5,111 (7.7%) influenza detections at clinical laboratories, from the 66,199 specimens collected last week. Of detected influenza viruses at public health laboratories last week, 58.8% were influenza A and 41.2% were influenza B. Among influenza A viruses, 56.7% were H3 and 43.3% were H1. CDC has reported an excellent match between circulating and vaccine strains (H3: 99%; H1: 100%; B: 100%) for this season. As of 4/06/2024, CDC estimates that there have been at least 33 million illnesses, 360,000 hospitalizations, and 23,000 deaths from flu. The percentage of primary care patients with influenza-like illness (ILI) declined to 2.8%, dropping below baseline. ILI activity is high in 1 state; Wisconsin has low levels. 138 pediatric deaths, due to influenza A (74), influenza B (62), and influenza A/B coinfection (2), have been reported for the 2023-2024 season to date.
Wisconsin has recorded 3,645 hospitalizations for influenza this season. This is lower than in 2019/2020 (3,968) and lower than 2022/2023 (3,531) at this point.
The performance of rapid influenza testing is moderate because of declining levels of circulating virus. RIDT(+) results may need to be confirmed using RT-PCR.
Viral causes of acute respiratory infections in Wisconsin primary care practices continued to be mixed with an abundance of Influenza B. For the week ending 4/06/2024, 3.4% of 12,380 specimens tested across Wisconsin by the Wisconsin State Laboratory of Hygiene and clinical labs were positive for SARS-CoV-2. About 1.1% of primary care patients are presenting with acute diarrheal illness. The most commonly identified gastopathogen is norovirus.
Over the past 4 weeks the typical ARI case has been 32.3 years old. 38% of patients have been female. 29% of patients identified a sick contact 1-3 days before illness onset and they typically present to the clinic 5.7 days after illness onset. 0% of illnesses are characterized as mild, with 86% having moderate symptoms and 14% having severe symptoms.
| Viruses in Circulation | Percent* in statewide laboratory surveillance | Percent** in primary care surveillance clinics |
|---|---|---|
| Influenza A | 32.7 | 0 |
| Influenza B | 29.0 | 50 |
| Seasonal Coronavirus*** | 1.8 | 0 |
| RSV | 6.2 | 0 |
| Parainfluenza | 1.6 | 50 |
| hMPV | 4.3 | 0 |
| Rhino/Enterovirus | 6.8 | 0 |
* The weekly influenza update is adapted from an email from Jon Temte, MD, PhD; Chair, Wisconsin Council on Immunization Practices; Professor, Department of Family Medicine and Community Health, University of Wisconsin School of Medicine and Public Health.
