It seems like every year we get early reports of the start of flu season.
Because a few people had positive flu tests somewhere…
Is Flu Season Starting Already?
While there are many things about the flu that are unpredictable, including when flu season will start, peak, and end, there are some things that have become rather routine.
One of the things that we have come to expect every year is folks declaring an early start to flu season.
Not surprisingly, they are usually wrong.
So why do some folks test positive in August or September if it isn’t because flu season is starting?
“During periods when influenza activity is low and there is low influenza virus circulation among persons in the community, the positive predictive value of influenza tests is low (that is, the chance that a positive result indicates that the patient has influenza is low – consider potential for a false positive result), and the negative predictive value is high (the chance that a negative result indicates that the patient does not have influenza is high – likely true negative result ).”
CDC on the Algorithm to assist in the interpretation of influenza testing results and clinical decision-making during periods when influenza viruses are NOT circulating in the community
When flu activity is low, such as it is during the summer or early fall before flu season has really started, you have a higher chance for a false positive flu test. So even though you have cold or flu symptoms and a positive rapid flu test, you might not really have the flu. The test is falsely positive. It’s wrong.
“Influenza prevalence varies between and within seasons. On the basis of our estimates, rapid tests are of limited use when prevalence is <10%”
Grijalva et al on Accuracy and Interpretation of Rapid Influenza Tests in Children
While other, more accurate flu tests are available, they are more expensive and take longer to process and get results. And since the diagnosis of the flu is often made clinically anyway, classic flu signs and symptoms during flu season, you typically don’t need a flu test unless being admitted to the hospital or if the results will really change how you are being treated.
While flu season usually starts in October, it is the peak that we are usually more concerned about. That’s when you are most likely to be exposed to someone and get the flu.
When does flu season usually peak?
It depends, but usually sometime between December and March, typically in February. Getting back to how unpredictable flu season can be, there have been a few times that flu season has peaked as early as October though.
How can you reduce your chances of having a false positive flu test?
More on the Start of Flu Season
- CDC – Flu Activity & Surveillance
- Flu Near You
- Flu Facts
- CDC – The Flu: What To Do If You Get Sick
- CDC – Flu Symptoms & Complications
- CDC – The Flu Season
- CDC – Current & Past Flu Seasons
- Your child tested positive for the flu. But does she really have it?
- CDC – Guide for considering influenza testing when influenza viruses are circulating in the community
- CDC – Algorithm to assist in the interpretation of influenza testing results and clinical decision-making during periods when influenza viruses are circulating in the community
- CDC – Algorithm to assist in the interpretation of influenza testing results and clinical decision-making during periods when influenza viruses are NOT circulating in the community
- CDC – Overview of Influenza Testing Methods
- CDC – Rapid Diagnostic Testing for Influenza: Information for Clinical Laboratory Directors
- CDC – Information for Clinicians on Rapid Diagnostic Testing for Influenza
- Study – Accuracy and Interpretation of Rapid Influenza Tests in Children
- Study – Diagnostic Accuracy of Novel and Traditional Rapid Tests for Influenza Infection Compared With Reverse Transcriptase Polymerase Chain Reaction: A Systematic Review and Meta-analysis
- Screening Tests – Cumulative Incidence of False Positives
- Why False Positive Results Are So Common In Medicine
- False Positives and False Negatives
- What Are False-Positive Test Results, and What Causes Them?
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