When kids get sick, pediatricians usually like to diagnose them with one single thing, so they usually wouldn’t diagnose strep and mono at the same time.
In most cases, though, mono is suspected in a child who tests negative for strep but has persistent symptoms.
Strep vs. Mono Tests
Tests can be done to evaluate a child for each infection, including:
A rapid strep test and throat culture for the group A Streptococcus bacteria
A heterophil antibody test (monospot) and Epstein-Barr virus (EBV) titer levels for mononucleosis
They aren’t usually all done at the same time, though, especially at the first sign that a child has a sore throat and fever.
Instead, a child who has already had a negative strep test returns to their pediatrician four or five days later because he isn’t getting better, and is then tested for mono.
Or a child who tested positive for strep is put on an antibiotic, such as amoxicillin, and develops a bad rash a few days later, which is characteristic of mono. But even if a child with strep doesn’t get a rash, he may just not get better, and still, get tested for mono.
So it is possible to have strep and mono at the same time, although one doesn’t necessarily cause the other. The more common scenario is that a child got infected with both by chance. The incubation period is four to seven weeks for mono and two to five days for strep, so your child would have had to be around someone with mono and strep at the right times, got infected, and then show symptoms of both infections at the same time.
Or it is possible that one or both of the tests were a false positive. A CDC investigation of a higher than normal number of strep throat cases at a clinic in Wyoming recently found that incorrect technique likely caused many strep throat tests to be falsely positive (they waited too long to read the tests).
Still, some experts do believe that you can have both strep and mono at the same time because these infections have a ‘synergistic effect’ on a child’s inflamed throat and tonsils, for example, making it more likely that you could become infected with mono while having strep. But while older studies found that 30 percent of patients with mono also had strep, some newer studies have found rates that were much lower, at only three or four percent.
Although it is sometimes hard to tell if a child has mono and strep when both tests are positive, or if he has mono and is a strep carrier, if he tests positive for strep, he will need antibiotics to prevent getting rheumatic fever. And since he has mono, this is one of the few situations in which it is important that your pediatrician carefully chooses which antibiotic to prescribe to your child. This is because amoxicillin or Amoxil, the antibiotic that is often used to treat kids with strep, can cause a bad rash if you take it when you have mono.
A more likely scenario is that a child with mono and strep is just a strep carrier. These are kids who had a strep throat infection and even though they are better and have no strep symptoms, the strep bacteria continue to live in the back of their throat.
Strep carriers are not thought to be contagious and they can test positive for strep for months or years, even when they have a sore throat that is being caused by a virus.