Rising Flu Cases: A Global Health Concern
Introduction
Influenza, commonly known as the flu, is a contagious respiratory illness caused by influenza viruses. With the recent surge in influenza cases worldwide, it is crucial to understand the current trends, symptoms, and preventive measures to protect public health.
Changes in Influenza Positivity Rates
Recent Trends
In recent weeks, there has been a notable increase in influenza positivity rates. In Canada, the positivity rate for the flu was at 19%, with case counts rising after a dip in January. The Public Health Agency of Canada reported a sharp increase in cases and positivity rates. In Quebec, about one in three tests were positive for the flu.
As of early February 2025, the test positivity for influenza in the US stood at 21% and was increasing. In the US, the percentage of respiratory specimens testing positive for influenza virus in clinical laboratories increased compared to the previous week, with some regions having positivity rates between 40% & 25%. Nationally in the US, during the 5th week this year, 31.6% of specimens tested in clinical labs were positive for influenza, compared to 12.8% positive cumulatively since the start of the season. The overall percentage of emergency department (ED) visits with a discharge diagnosis of influenza increased compared to the previous week.
Global Influenza Rates
Worldwide Impact
Globally, influenza continues to be a major health concern. The U.S. appears to be experiencing one of its most intense flu seasons in recent years. The U.S. winter virus season is in full force, and by one measure, it is the most intense in 15 years. The Southern Hemisphere had an earlier flu season than the Northern Hemisphere, and data suggests this season’s shots offered only modest protection, with vaccines reducing the risk of flu-related hospitalizations by about 35% among high-risk groups. In Canada, flu activity was "widespread" in British Columbia, Ontario, and Quebec.
Influenza Rates in the U.S.
U.S. National Overview
In the United States, influenza activity remains elevated across most of the country. At least 24 million people in the U.S. have caught the flu so far this season. Nearly 8% of U.S. outpatient medical visits recorded during the week ending Feb. 1 were related to respiratory illnesses, including the flu. Forty-five states and territories are currently seeing "high" or "very high" flu activity. The CDC estimates that there have been at least 24 million illnesses, 310,000 hospitalizations, and 13,000 deaths from flu so far this season. The weekly hospitalization rate observed during Week 5 was 9.2 per 100,000 population. The weekly hospitalization rates observed during Week 1 and Week 4 (10.2 per 100,000 population) are tied with the 2017-2018 season as the highest peak weekly rate observed across all seasons since 2010-2011. A total of 19,609 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2024, and February 1, 2025. Nationally, during Week 5, 48,661 laboratory-confirmed influenza-associated hospitalizations were reported.
Ten pediatric deaths associated with seasonal influenza virus infection were reported this week, bringing the 2024-2025 season total to 57 pediatric deaths. Based on NCHS mortality surveillance data available on February 6, 2025, 2.0% of the deaths that occurred during the week ending February 1, 2025 (Week 5), were due to influenza.
Signs and Symptoms of Influenza
Recognizing the Flu
Influenza symptoms can range from mild to severe and often come on suddenly. Common signs and symptoms include fever or feeling feverish/chills, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue (tiredness), and some people may experience vomiting and diarrhea, which is more common in children than adults.
Rates of ICU or Critical Care Admissions
Severe Cases
The severity of influenza can lead to critical care admissions. In Alberta, there have been 1,298 hospitalizations and 101 intensive care unit admissions due to influenza so far this season. In Quebec, some flu cases have ended up in the ICU. For several years up until 2023, about 10 to 20 percent of children admitted to pediatric hospitals for influenza needed intensive care. Any person with laboratory-confirmed influenza admitted to an intensive care unit (ICU) or requiring mechanical ventilation is counted as an ICU admission. The cumulative rate (per 100,000 population) of influenza-associated ICU admissions is tracked weekly.
Public Interventions to Reduce Influenza Risk
Preventive Measures
To reduce the risk of contracting influenza, there are several interventions you can consider.
Vaccination, despite some contention about vaccines, is is still the best defence against the flu, even in the middle of the season.
Getting a vaccine reduces the risk of flu illnesses that require a medical visit "by about half" through mid-January. Also, if you live in Canada, CBC reports that the federal government has just purchased 500, 000 doses of the Avian Flu vaccine targeted to high risk people, or those most likely to be exposed.
Wearing a mask in high-risk situations can help protect against the flu. Masks can also be worn preventatively in crowded indoor settings.
If you think or feel you are already sick, it is important to stay home to avoid spreading the virus. Avoid close contact with people who are sick.
Washing hands with soap and water helps prevent the spread of germs. If you can find soap and water, alcohol based spray hand sanitizer is a great option to sanitize in your hands and other surfaces (handles, door knobs, elevator buttons, etc)
Avoid touching your eyes, nose, and mouth, as germs can spread that way. Regularly clean and disinfect surfaces that are often touched.
A person at high risk of complications may want to consider getting a prescription for an antiviral medication early on in their illness. Antiviral drugs for the flu are most effective when taken early in an illness.
Conclusion
The rising cases of influenza globally and in the U.S. underscore the importance of vigilance and preventive measures. By staying informed and taking proactive steps, we can reduce the impact of influenza on our communities and protect public health.