Why are throat swabs incubated anaerobically

Age was later added in the modified McIsaac score [ 3 ]. There are substantial differences among guidelines from different countries, regarding the need of culture or RADT for the diagnosis of GAS and regarding the need to prescribe antibiotic as a treatment. On the other hand, guidelines from Belgium, the Netherlands, England and Scotland consider throat pain as a self-limiting disease therefore culture and antibiotic treatment are not recommended. Israeli guidelines are in line with North American guidelines [ 10 ].

Accurate diagnosis is significant for two reasons; it is important to recognize patients with GAS for the prevention of acute rheumatic fever and suppurative complication. However, it is also essential to recognize patients without GAS for reducing unnecessary antibiotic prescription, which is a rising problem worldwide [ 11 , 12 ].

The reliability of throat culture depends on several variables including the swabbing site within the pharyngeal-oral cavity, the use of anaerobic incubation conditions, selective culture plates and duration of incubation [ 1 ].

The Infectious Diseases Society of America IDSA states that throat swab specimens should be obtained from the surface of either tonsils or tonsillar fossae or the posterior pharyngeal wall. Other areas of the oral pharynx and mouth are not considered as acceptable sites [ 1 ]. Use of anaerobic incubation and selective culture media can increase the likelihood of detecting GAS if present [ 13 ]. The aim of this study was to compare cultures from swabs obtained from the buccal surface and the tongue mouth culture with cultures from swabs obtained from the tonsils and posterior oropharynx throat culture for the diagnosis of GAS pharyngitis in both children and adults.

We conducted a prospective study that compared mouth and throat cultures. Eleven family physicians from 11 different MHS clinics in the southern district of Israel collected cultures from consecutive patients, with a clinical picture of GAS pharyngitis who agreed to participate and signed informed consent.

Patients suspected to be GAS carriers i. Informed consent was signed by the patient or his guardian for children prior to sample collection. Two swabs were obtained from each patient; one from both sides of buccal surface and the front of the tongue mouth culture and the second from the tonsils and oropharynx throat culture, the gold standard.

RADT was not performed. No other additional tests were performed including respiratory virus tests. All cultures were collected by physicians participating in the research.

Physicians treated patients according to clinical diagnosis and once received the results of the throat cultures, treatment was adjusted accordingly. Results of the mouth culture were documented in a separate file and were known solely to the laboratory manager and the primary researcher. Swabs were cultured on Strep A selective agar Novamed ltd.

In addition, an antibiotic disc Bacitracin 0. Lancefield group A antigen test was not used. Israel was used. In this study we analyzed two different groups — children and adults.

Thus sample size calculation applies to each group separately. We used Stata, version Likelihood ratios were calculated using the substitution formula, where 0. Eleven family physicians from MHS in the southern district of Israel collected swabs from patients who agreed to sign informed consent, between November and March Patients were divided to two groups: pediatric patients and adult patients.

Prevalence of GAS pharyngitis was The results of throat and mouth cultures of pediatric patients are presented in Table 1. Sensitivity of the mouth culture was The results of throat and mouth cultures of adult patients are presented in Table 1. All patients in our study improved with antibiotic treatment provided in the community, and no patient was admitted to the hospital due to complications. In our study we demonstrated mouth swab culture sensitivity of This finding supports the IDSA recommendation that the optimal site for culture is the posterior oropharynx or the tonsils.

However, our findings challenge the statement that other sites in the oral cavity are not acceptable. The sensitivity of mouth culture in children was close to the sensitivity of RADT. For adults the sensitivity was slightly, but not significantly lower, possibly due to lower bacterial load in the oral cavity.

Swabbing the tonsils is a very common exam in the office of the primary care physician, with an unpleasant effect on children, causing distress and often gag reflex. Therefore, swabbing of the mouth may be a good alternative for the gold standard swabbing technique. With excellent specificity, if the result is positive, the physician can be sure he received the correct result.

However, in case of a negative result, throat culture will be necessary to exclude the diagnosis, similar to common practice with RADT. This approach may be unacceptable for some physicians due to the need of a second visit. Further research is needed to test oral swabbing using RADT or molecular test with immediate results. In this approach, a positive result will be accepted and a negative result will require an oropharyngeal culture at the same visit.

Our study has several strengths, including large sample size of children and adults, the participation of 11 family physicians from different clinics, a single microbiological laboratory that examined all cultures and the use of newer microbiological techniques than those used in prior studies.

A potential limitation of our study is the lack of RADT and molecular test in comparison to culture and lack of calculation of inter-clinician variation in swabbing accuracy. The IDSA recommendation about optimal site of throat culture is based on very limited amount of studies. Two studies conducted by Brien et al. Both studies showed significant superiority of cultures from optimal sites.

As noticed in both studies, swabs from the oral cavity were not always negative and had some detection of GAS, though with unsatisfactory sensitivity. The most predominant limitations in both studies are the small numbers and the time interval between the first and second culture.

Microbiological technology for cultures has improved and results from studies using older techniques are less relevant today. Two later studies carried out in — further examined the question of optimal swabbing location see Table 2. Fox et al. Each child underwent double swab collection, a throat swab from the posterior pharynx and tonsils and a mouth swab the tongue and buccal mucosa. Has PDF. Publication Type. More Filters.

Effect of atmosphere and duration of incubation on primary isolation of group A streptococci from throat cultures. View 1 excerpt, cites background. Suitability of throat culture procedures for detection of group A streptococci and as reference standards for evaluation of streptococcal antigen detection kits. Atypical Streptococcus pyogenes from an ear discharge.

Detection of group A streptococci in the laboratory or physician's office. Culture vs antibody methods. Suitability of a throat culture method for evaluation of group A streptococcal antigen detection kits. Primary plate identification of group A Streptococcus on a selective medium. Efficiency in an office practice.

Comparative evaluation of selective and nonselective culture techniques for isolation of group A beta-hemolytic streptococci.

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