Strep throat epidemiology and demographics
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Sensitivity & Specificity
A study of 729 patients with pharyngitis in which 17% had a positive throat culture for group A streptococcus, identified the following four best predictors of streptococcus[1]:
1. Lack of cough
- sensitivity = 56%
- specificity = 74%
2. Swollen tender anterior cervical nodes 3. (Marked) tonsillar exudates. Although the original study did not specify the degree of exudate, 'marked exudate' may be more accurate. A subsequent study of 693 patients with 9.7% having positive cultures found that 'marked exudates' had a sensitivity and specificity of 21% and 70% while 'pinpoint exudates' were nonspecific with sensitivity and specificity of 22% and 45%[2].
- sensitivity = 65%
- specificity = 69%
4. History of fever
- sensitivity = 78%
- specificity = 45%
5.hurts when swallowing.
When these findings are counted in a patient, the probabilities of positive cultures in the original study (prevalence=17%) are[1]:
- 4 findings -> 55.7%
- 3 findings -> 30.1 – 34.1%
- 2 findings -> 14.1 – 16.6%
- 1 findings -> 6.0 - 6.9%
- 0 findings -> 2.5%
The probabilities can also be computed with the following equation: X = −2.69 + 1.04 (exudtons) + 1 (swolacn) - 0.95 (cough) + 0.89 (fevhist)
References
- ↑ 1.0 1.1 Centor RM, Dalton HP, Campbell MS, Lynch MR, Watlington AT, Garner BK. Rapid diagnosis of streptococcal pharyngitis in adult emergency room patients. J Gen Intern Med. 1986 Jul-Aug;1(4):248-51. PMID 3534175
- ↑ Komaroff AL, Pass TM, Aronson MD, Ervin CT, Cretin S, Winickoff RN, Branch WT Jr. The prediction of streptococcal pharyngitis in adults. J Gen Intern Med. 1986 Jan-Feb;1(1):1-7. PMID 3534166