Recovering Streptococci from the Throat, a Practical Alternative to Direct Plating in Remote Tropical Communities

Abstract

Throat swabs are regarded as the "gold standard" for diagnosing streptococcal pharyngitis and for surveillance research. Culturing throats in remote tropical settings is logistically difficult, and these settings are commonly burdened by high rates of streptococcal disease. The survival of streptococci on swabs may depend on whether they are of "throat" or "skin" type, as determined by emm pattern typing. The aims of this study were to compare the recovery rates of beta-hemolytic streptococci (BHS) using three different transport methods and to determine whether the recovery rates correlated with the emm pattern type. Monthly duplicate throat swabs were taken from occupants of selected households in three remote Aboriginal communities. Paired swabs were separated and handled in one of three ways: (i) direct inoculation onto culture media with cold-box transport (plated), (ii) sealed in a bag with a silica gel desiccant and cold-box transport (desiccant), and (iii) transport at ambient temperature and humidity (ambient). emm pattern typing was done by standard methods. Over 23 months, 4,842 throat swabs were taken, and 4,122 were paired. BHS were recovered on 11.5% of the 4,842 occasions (group A, 4.5%; group C, 1.7%; group G, 5.4%). Results from paired swabs showed the plated method was superior to desiccant and desiccant was better than ambient. Pooled data indicated that plated and desiccant were equivalent, and both were significantly better than ambient. There was no correlation between the emm pattern type and recovery of group A streptococci by different methods. In tropical and remote settings, cold-box transport with desiccant and subsequent inoculation of culture plates in the laboratory is a practical alternative to direct plating.There are two reasons for swabbing the throat to recover beta-hemolytic streptococci (BHS)-for diagnosis of streptococcal pharyngitis as part of clinical management, and for research purposes. Even in the best of circumstances, throat swabs and cultures have limitations; these include variability of sampling, lack of standardized laboratory methods, difficulties with interpretation in an asymptomatic carrier, and a relatively long turnaround time (12,17,24). Tropical and remote settings pose particular challenges for getting throat swabs to laboratories; these include high temperatures and humidity, the frequent need to collect specimens in the outdoors, limited local infrastructure (including refrigeration), difficult communications, and long distances for transportation of materials and specimens (35). Laboratory facilities are often the least accessible in places where the burdens of streptococcal disease and postinfectious sequelae are highest.The development of rapid antigen tests for group A betahemolytic streptococci (GAS) in the 1980s promised to facilitate rapid diagnosis. However, antigen testing may not be practical or cost-effective in many resource-poor settings with high rates of BHS infection (22). Newer tests, including gene probe technology and real-time PCR,...

Use of a Single-Nucleotide Polymorphism Genotyping System To Demonstrate the Unique Epidemiology of Methicillin-Resistant Staphylococcus aureus in Remote Aboriginal Communities

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