An Evaluation of Methods for Culturing Group A Streptococci from the Pharynx

Abstract

N EW METHODS which promise more accurate diagnosis of group A streptococcal infeictions of the pharynx are worthy of note for two reasons: First, prompt diagnosis permits the beginning of appropriate antimicrobia.l therapy, the effectiveness of which precludes suppurative complications (1). Second, as Ramnielkamp and others (1, 2) have clearly demonstrated, the eradication of streptococci within a period of 9 days or less after onset of infection prevents the development of rheumatic fever. Diagniosis of group A streptococcal infections, based on clinical findings, alone, may be accurate in 70 percent of all cases but frequently is less reliable (3). The proper use of current laboratory methods adds significantly to the validity of the diagnosis, although no method permits 100 percent accuracy (4). Phvsicians can be expected to improve their diagnostic skill by systematically correlating clinical observations and laboratory findings, but the achieveinent of highest possible accuracy in the identification of group A streptococcal infections rests on the continued improvement of bacteriological techniques. In a recent review, Stollerman (5) has summarized the culturing methods presently considered to, be most effective. Although certain modifications in bacteriological techniques may improve the accuracy in diagnosing streptococcal infections, they often are achieved at the cost of complexity and higher expense and consequently are of relatively limited value in clinical practice. Ideally, improvements should be directed tolward greater reliability of these methods and at the same time be easily adaptable for use in clinical laboratories or in physicians' offices. This study was designed to evaluate various methods, several of them easily applicable in clinical practice, for the bacteriological diagnosis of group A streptococcal infections of the pharynx. Our study was based on two previous investigations. The first, by Joe (6), showed that enteric pathogens survived for considerable periods of time in the dry state on filter paper, whereas nonpathogens of the same species did not survive. Hollinger and Lindberg (7, 8) applied this approach, with dacron swabs and filter paper strips, to the identification of group A streptococcal infections and demonstrated that these organisms could be recovered with relative ease after drying on filter paper, whereas most other organisms found in the throat do not survive. As a result of the Hollinger and Lindberg report, a specially designed Dr. McFarland is clinical instructor and Mrs. A below is senior instructor, department of internal medicine, University of Colorado School of Medicine, Denver. Mrs. Blomstrom was a laboratory assistant at Fort Carson, Colo. Dr. Glaser is president of the Afflliated Hospitals Center, Boston, Mass., and professor of social medicine at the Harvard Medical School, He was dean and professor of medicine at the University of Colorado School of Medicine when this work was done. This study was supported in part by a grant from the Life Insurance Medical Research Fund.