False Negatives On Strep Tests?

Dear Ask The Doctor: When I was five I came down with strep. It came back negative on a throat culture so I was not treated with antibiotics, and was sent home. I became increasingly ill and eventually after some blood work was ordered I was diagnosed with rheumatic fever. Since then I have had a case of strep about once a year every year for the last 25. 99% of the time the symptoms will be absolutely classic according to the physician, but the throat cultures still come out negative. Even when they grow the rapid test out over a few days, they are still negative. Generally I end up back in the doctor's office a few days later when my symptoms have gotten worse; a few times I have ended up in the ER. The last time they had to put me on intravenous fluids and give me shots of antibiotics because I had a fever of close to 105 and a throat so swollen I was unable to swallow saliva. Is there any reason why throat cultures would always come back negative on someone who has strep? It concerns me that that so often I end up becoming very seriously ill before I am treated because of what the tests are missing.

Dear Kate:

The rapid strep test can give false-negative results even when strep bacteria are present. When the results of a rapid strep test are negative, many health professionals recommend doing a throat culture to make sure that strep throat is not present.

On the other hand a culture that does not grow any bacteria or fungus generally means that you either have a viral infection or that an infection is not present. Other factors, such as the amount of sample, the timing of the sample, the type of culture done, and recent use of antibiotics can prevent the growth of bacteria or fungus in the culture. In your case since you had a documented infection, certain factors such as Contamination of the throat culture sample by other types of bacteria from the mouth or if you were Using antiseptic mouthwashes before the culture is taken might have affected too the results of your sample.