Several different things can cause an annoying and sometimes really painful sore throat — bacteria, viruses, bacteria, allergens and fungi to name a few.
Here, a physician offers some information about how healthcare providers figure out if your sore throat is caused by one of the nastiest reasons of all: strep.
The question, and what the doctor says
The question: I took my daughter to the doctor with a fever of 99 degrees Fahrenheit and a sore throat, and they didn’t test her for strep throat. Why is that?
Throat swab tests and other signs of strep
Dr Gerhart answers: The practice of doing a throat swab for sore throat varies among urgent care centers and clinics. Some centers test any child with a sore throat, which is likely over-testing, while other centers have the health care provider first look at the throat and assess the child’s symptoms before deciding on testing.
When people use the term strep throat, they are usually referring to an infection caused by group A streptococcus, a type of bacteria responsible for up to 30 percent of sore throats in kids. Most of the other 70 percent of sore throats are caused are viruses.
When assessing your child for strep throat, physicians are taught to follow the “Modified Centor Criteria,” clinical factors that predict the likelihood of a strep infection. These factors are:
- Absence of cough
- Swollen and tender lymph nodes
- Temperature greater than 100.4 F
- Swollen tonsils or white/red dots on the tonsils; these are called tonsillar exudates
- Age younger than 14 years old
Each of these factors is given one point. A cumulative score of zero or one is considered “low risk,” with only 1 to 10 percent of these cases having a group A streptococcal infection. Chances are that these patients have a viral illness causing their sore throat, and they do not need strep testing.
On the other hand, 11 to 35 percent of people with a score of two or three do have a group A strep infection, and should be tested. Those with a score of four or five have more than a 50 percent chance of strep infection, and may be treated with antibiotics without testing.
There are two main types of strep tests.
The first is the “rapid antigen detection test” (a version of which is shown at right), which usually is back in about five minutes. This test is positive in about 90-99 percent of group A strep cases.
If the rapid test is negative, your doctor usually orders the sample to be cultured — a second round of testing. Sometimes the rapid test is falsely negative, and the culture comes back positive in 24 to 48 hours.
Not everyone needs to be treated
So why not test and treat everyone? Well, the justification to treat group A strep is not just to help you feel better — it’s actually to prevent complications of the infection.
Most strep throat infections are self-limited, and get better within five to seven days without treatment. Antibiotics shorten symptom length by only about 16 hours, and often give only mild relief of symptoms during that time. Plus, widespread use of antibiotics may cause the bacteria to become resistant to that antibiotic, giving us fewer options with which to treat it in the future.
However, often day care centers and schools will not let kids return until they are on antibiotics and considered “not contagious,” usually 24 hours after starting antibiotics.
Perhaps the larger reason to use antibiotics for strep is to prevent complications like an abscess in the tonsils, infection in the kidneys, or rheumatic fever. Rheumatic fever — a big concern in earlier decades — was caused by an untreated strep infection, and resulted in scarring of the heart valves. Now that we are treating strep with antibiotics, rheumatic fever is very rare.
So testing for strep depends on your child’s symptoms (or lack of symptoms), age, condition and your physician’s own practice.
In general, if your child has a fever and a sore throat without any other symptoms of a cold (cough, runny nose, congestion), your provider will likely test him or her. You should let your child’s doctor know if the symptoms are not improving after five to seven days, regardless of treatment.