Your child tested positive for the flu. But does she really have it?
The Doc Smitty and why all flu tests aren't the same
“Dr. Smith, I just got a call from a family who needs you to call an order in for Tamiflu for them because their 5 year old just tested positive for flu.”
There are a lot of reasons I didn’t want to do this:
- I was in the office seeing patients and you chose to go to elsewhere. This family had taken their child to a quick in-and-out urgent care center. Not even a Cook Children’s Urgent Care. (Hey, I’m human and I have feelings too. But, I can get past you taking your child somewhere else first, if it was in the best interest of the family.)
- I don’t routinely treat family members to prevent the flu. If they are high risk with asthma or other chronic medical conditions, maybe. But the whole family? What about next month when someone else gets the flu? Monthly Tamiflu for the family?
- Finally, the one that made me the most upset, this phone call came in August!
Why does that matter?
Flu is a seasonal disease. We typically start seeing flu sometime in late October or in November, but this is not always predictable.
Morgan Pence, Ph.D., a clinical microbiologist at Cook Children’s, says that we should “expect to start seeing it in the next two to three weeks, but it's hard to say because flu season fluctuates every year. There have been years where it hasn't really hit until mid to late December.” So far, Cook Children’s medical center has not had a positive test for flu.
There are two main tests that we use to diagnose flu. One test is more accurate but it takes more time and is more expensive. It is run in hospitals.
The other test is cheaper and faster but the results are not as reliable. This is the test that is run in physicians’ offices and urgent care clinics. It can also be run in hospitals as well, when rapid testing is indicated, but Cook Children’s does not run this test after April until flu activity actually starts in the late fall.
The reason goes back to the characteristics of the test. Almost no test in medicine is 100 percent reliable. With all tests, there is a risk of a child having the disease, but testing negative and vice versa. The reliability of the test changes a lot depending on how many cases of the disease are in the community at the time.
Flu tests that are positive when flu activity is low are more likely to be wrong. This is less common but still possible.
Flu tests that are negative when your child has the right symptoms and flu activity is high are probably also wrong. This is one of the reasons that the Center for Disease Control and Prevention gives us the option to treat flu based on symptoms alone when activity is at its highest.
What did I do with my flu positive family?
I asked the dad to bring the child over and took a good history and physical. This took quite a bit of convincing that this was the right thing to do since they had already paid for a doctor’s visit elsewhere that day, so I promised to do it for free.
Turns out, the child’s symptoms were actually pretty weak for flu. I spent time explaining why the test was likely inaccurate and why I would not recommend treating him or his siblings for flu.
When my nurse called back the next day, the child was back at school and his family was $100s richer than they would have been.