Throat Culture For Group Research Articles

Agreement between rapid antigen detection test and culture for group A streptococcus in patients recently treated for pharyngotonsillitis - a prospective observational study in primary care

Objective The aim was to compare rapid antigen detection test (RADT) and throat culture for group A streptococci (GAS) among patients recently treated with penicillin V for GAS pharyngotonsillitis. Design and setting The study was a secondary analysis within a randomized controlled trial comparing 5 versus 10 days of penicillin V for GAS pharyngotonsillitis. Patients were recruited at 17 primary health care centres in Sweden. Subjects We included 316 patients ≥ 6 years of age, having 3–4 Centor criteria, a positive RADT and a positive throat culture for GAS at inclusion, and also having a RADT and throat culture for GAS taken at a follow-up visit within 21 days. Main outcome measures RADT and conventional throat culture for GAS. Results This prospective study showed 91% agreement between RADT and culture at follow-up within 21 days. Only 3/316 participants had negative RADT with a positive throat culture for GAS at follow-up, and 27/316 patients with positive RADT had a negative culture for GAS. Log rank test did not reveal any difference in the decline over time of positive tests between RADT and throat culture (p = 0.24). Agreement between RADT and throat culture for GAS at the follow-up was not associated with treatment duration, number of days from inclusion until follow-up, throat symptoms at follow-up, gender, or age. Conclusion RADT and culture for GAS agreed to a high extent also after recent penicillin V treatment. RADT for GAS means a low risk for missing the presence of GAS. KEY POINTS Testing for group A streptococci (GAS) before antibiotic treatment can reduce antibiotic prescription for pharyngotonsillitis. It has been proposed that rapid antigen detection tests (RADT) for group A streptococci after recent penicillin V treatment may be falsely positive due to possible persisting antigens from non-viable bacteria. The decline of the presence of GAS was similar between RADT and conventional throat culture in patients who had recently completed penicillin V treatment for GAS pharyngotonsillitis RADT for GAS is useful in identifying the presence of GAS after recent penicillin V treatment

Sore throat in primary care project: a clinical score to diagnose viral sore throat.

Objective.Viral agents cause the majority of sore throats. However, there is not currently a score to diagnose viral sore throat. The aims of this study were (i) to find the rate of bacterial and viral causes, (ii) to show the seasonal variations and (iii) to form a new scoring system to diagnose viral sore throat.Methods.A throat culture for group A beta haemolytic streptococci (GABHS) and a nasopharyngeal swab to detect 16 respiratory viruses were obtained from each patient. Over a period of 52 weeks, a total of 624 throat cultures and polymerase chain reaction analyses were performed. Logistic regression analysis was performed to find the clinical score.Results.Viral infection was found in 277 patients (44.3%), and GABHS infection was found in 116 patients (18.5%). An infectious cause was found in 356 patients (57.1%). Rhinovirus was the most commonly detected infectious agent overall (highest in November, 34.5%), and the highest GABHS rate was in November (32.7%). Analysis of data provided a scoring system, called the Mistik Score, to diagnose viral sore throat. The predictive model for positive viral analysis included the following variables: absence of headache, stuffy nose, sneezing, temperature of ≥37.5°C on physical examination, and the absence of tonsillar exudate and/or swelling. The probability of a positive viral analysis for a score of 5 was 82.1%.Conclusion.The Mistik Score may be useful to diagnose viral sore throat. We suggest its use either alone or in combination with the Modified Centor Score.

Validation and Modification of Streptococcal Pharyngitis Clinical Prediction Rules

To validate a simplified version of the Walsh clinical prediction rules (CPRs) for the presence of streptococcal pharyngitis in an inner-city, ethnically diverse population. This prospective study conducted in New York City, NY, from January 1,1997, to May 31,1997, consisted of 171 consecutive adult walk-in patients who presented with symptoms of upper respiratory tract infection and/or sore throat. The patients were assessed by using 5 clinical factors: cough, exposure to known streptococcal contact, temperature, tonsillar-pharyngeal exudates, and cervical lymphadenopathy. Throat cultures for group A beta-hemolytic streptococcus were obtained from all patients. Clinicians assessing the patients were unaware of throat culture results, and those processing the throat cultures were blinded to the clinical predictors. The prevalence of streptococcal pharyngitis was 24% (95% confidence interval, 18%-30%). The simplified version of the Walsh CPR for streptococcal pharyngitis predicted accurately the probability of a positive culture in our diverse population (area under the receiver operating characteristic curve, 0.71). The simplified CPR also showed clinically useful likelihood ratios and posterior probabilities. A simplified version of the Walsh CPR is accurate for diagnosing streptococcal pharyngitis in an inner-city population. This finding should provide clinicians more confidence in applying the CPR in similar clinical settings.

A 16-year-old boy with rapidly progressing pulmonary fibrosis

A 16-year-old boy with no chronic medical illness was evaluated for fever, cough, shortness of breath, and epigastric pain exacerbated by inspiration. Nine days before this admission, the patient had a sore throat, vomiting, diarrhea, and decreased intake of fluids because of mouth sores. After 2 days of illness, he was admitted with dehydration to a local hospital. His blood urea nitrogen was 86 mg/dL, and his creatinine was 8.4 mg/dL. Renal failure was attributed to either acute tubular necrosis or to poststreptococcal glomerulonephritis. Additional studies during this first admission included a white blood cell count of 18,000 cells/mm3, proteinuria of >300 mg/dL, and an elevated circulating C3 component of complement of 127 mg/dL (reference range: 51-95 mg/dL). Blood culture, urine culture, and throat culture for group A β-hemolytic streptococci were all negative, as were tests for antinuclear antibody, antistreptolysin O antibody, heterophile antibody, and stool culture. A renal ultrasonogram was normal. The patient received intravenous fluid therapy and was discharged after 5 days with an improvement of his blood urea nitrogen to 21 mg/dL and creatinine level of 2.1 mg/dL. Two days later, the patient sought emergent care for the new onset of respiratory symptoms, the return of diarrhea, and one episode of hematemesis. The patient lived on a farm with his parents and 2 siblings. He denied drinking alcohol, smoking tobacco, and taking illicit drugs.

Group A streptococcal carriage: Can the troll be tamed?

The dilemma of determining optimal care for the child with repeatedly positive throat cultures for group A beta hemolytic streptococcus (group A strep) has bedevilled paediatricians, family practitioners and generalists for decades. Unfortunately, the state of the art has not changed substantially over the past 20 years, as attested to by the dearth of publications and the similarity of the definitive recommendations spanning that period (1,2). The purpose of this column is to review briefly the state of knowledge about chronic streptococcal carriage and to suggest a rational approach to treating children who present with this problem. The challenge of evaluating a child with a positive throat culture for group A strep results from the inability to distinguish between the carrier (one who harbours the organism without a host response) and the child who is acutely infected (one who has evidence of inflammation and host response). Carriers are often identified when they continue to harbour the organism in the throat asymptomatically after an appropriate 10-day course of penicillin or alternative agent (3). There is a high rate of carriage in the general population (approximately 5% to 15% of school-aged children are colonized but not infected with group A strep at any time), and there is no foolproof way to differentiate a priori between carriers and those who are acutely infected. Therefore, many children are diagnosed with streptococcal pharyngitis who are chronic carriers and who are probably acutely infected with another organism (such as a respiratory virus). In this era of evolving antibiotic resistance and a desire to limit unnecessary use of antimicrobial agents, a logical strategy for avoiding therapy of chronic carriers is required. Chronic carriers of group A strep probably do not pose a threat to themselves or to others. There is no evidence that these children or their contacts become infected with the strains that these children carry. Therefore, they do not require antibiotic therapy to prevent suppurative or nonsuppurative (acute rheumatic fever, acute poststreptococcal glomerulonephritis) complications. So why do doctors need to worry? The simple answer is that physicians are unable to differentiate at presentation between the child who is acutely infected and the one who is a chronic carrier presenting with acute nonstreptococcal pharyngitis. The methods for making that discrimination (testing for serological response and strain typing) require time and the aid of reference or research laboratories. What can the medical practitioner do when confronted with a child who repeatedly returns to the office or clinic for evaluation of or therapy for acute respiratory illnesses in which group A strep is recovered from the throat? If it could be determined a priori whether that child is a streptococcal carrier, antibiotic therapy could be avoided. A child is likely a carrier if he or she has symptoms most consistent with a viral upper respiratory infection and has consistently harboured group A strep in the past. However, the discriminatory power of clinical evaluation of such patients is notoriously unreliable. Perhaps the most expedient strategy is to attempt eradication of the carrier state. If successful, ie, the child has a negative culture after completion of therapy, one might assume that if the child presents again with pharyngitis and a throat culture positive for group A strep, this is evidence of bone fide acute streptococcal infection. Eradication of carriage should probably be reserved for children who remain culture-positive after a full and appropriate course of antibiotic therapy, and who have had at least three symptomatic episodes of pharyngitis with

Effectiveness of clinical guidelines for the presumptive treatment of streptococcal pharyngitis in Egyptian children.

Primary prevention of acute rheumatic fever requires antibiotic treatment of acute streptococcal pharyngitis. In developing countries, clinicians must rely on clinical guidelines for presumptive treatment of streptococcal pharyngitis since bacterial culture and rapid diagnostic tests are not feasible. We evaluated the WHO Acute Respiratory Infection guideline in a large urban paediatric clinic in Egypt. Children between 2 and 13 years of age who had a sore throat and pharyngeal erythema were enrolled in the study. Clinical, historical, and demographic information was recorded and a throat culture for group A beta-haemolytic streptococci was done. Sensitivity (% of true-positive throat cultures) and specificity (% of true-negative throat cultures) were calculated for each clinical feature. The effect of various guidelines on correct presumptive treatment for throat-culture status was calculated. Of 451 children with pharyngitis, 107 (24%) had group A beta-haemolytic streptococci on throat culture. A purulent exudate was seen in 22% (99/450) of these children and this sign was 31% sensitive and 81% specific for a positive culture. The WHO Acute Respiratory Infections (ARI) guidelines, which suggest treatment for pharyngeal exudate plus enlarged and tender cervical node, were 12% sensitive and 94% specific; 13/107 children with a positive throat culture would correctly receive antibiotics and 323/344 with a negative throat culture would, correctly, not receive antibiotics. Based on our data we propose a modified guideline whereby exudate or large cervical nodes would indicate antibiotic treatment, and this guideline would be 84% sensitive and 40% specific; 90/107 children with a positive throat culture would correctly receive antibiotics and 138/344 with a negative throat culture would, correctly, not receive antibiotics. The WHO ARI clinical guideline has a high specificity but low sensitivity that limits the unnecessary use of antibiotics, but does not treat 88% of children with a positive streptococcal throat culture who are at risk of acute rheumatic fever. A modified guideline may be more useful in this population. Prospective studies of treatment guidelines from many regions are needed to assess their use since the frequency of pharyngitis varies.

Randomized evaluation of benzathine penicillin V twice daily versus potassium penicillin V three times daily in the treatment of group A streptococcal pharyngitis

In a randomized, prospective, multicenter study the clinical and bacteriological efficacies of three dosage schedules with two different salts of oral penicillin V suspensions (regimen 1: potassium salt of penicillin V, 50,000 U/kg of body weight per day in three divided doses; regimen 2: benzathine salt of penicillin V, 50,000 U/kg of body weight per day in two divided doses; and regimen 3: benzathine salt of penicillin V, 100,000 U/kg of body weight in two divided doses) for the treatment of streptococcal pharyngitis were evaluated. Children with clinical signs of acute pharyngitis and a positive throat culture for group A beta-hemolytic streptococci (GABHS) were eligible. There was no difference between the treatment groups with respect to the overall clinical success rate. Eradication of the original serotype of GABHS from throat cultures was achieved in 87.1% (regimen 1), 85.5% (regimen 2) and 87.7% (regimen 3) of patients. The incidence of potential drug-related adverse events was significantly higher in patients treated with regimen 3. The results of this and earlier studies strongly suggest that oral penicillin given twice daily should be the recommended treatment for the initial treatment of pharyngitis due to GABHS. Doubling the total daily dose is not beneficial in the usual clinical setting. Because of its favorable pharmacokinetics, the benzathine salt of penicillin V appears to be well suited for a twice-a-day dosage schedule.

Pathological Cases of the Month

A 13-YEAR-OLD Korean boy had a 1-month history of recurrent fever, leukopenia, and bilateral cervical lymphadenopathy. One month prior to presentation, he had a 10-day illness: sore throat, abdominal pain, and daily fever spikes to 40°C. White blood cell count at that time was 2.2× 10 9 /L (polymorphonuclear cells, 0.24; band forms, 0.37; lymphocytes, 0.32; and monocytes, 0.07). Throat culture for group A β-hemolytic streptococcus was negative, as were a slide agglutination test for heterophil antibodies to Epstein-Barr virus and testing for IgG- and IgM-specific serum antibodies to Epstein-Barr viral capsid antigen. For 6 days prior to admission, temperature to 40°C and sore throat recurred; anorexia and fatigue developed. He had lost 2.2 kg in the last month. On examination, his oral temperature was 39.0°C. He appeared tired but not acutely ill. He had bilateral anterior and posterior cervical lymphadenopathy; these soft, mobile, nontender lymph nodes were 0.5 to

Throat Cultures

I read with great interest the article entitled "Duration of Positive Throat Cultures for Group A Streptococci After Initiation of Antibiotic Therapy" by Snellman et al.1 The study involved 47 patients in whom streptococcal pharyngitis was diagnosed, who were randomly selected to receive three different antimicrobial regimens with a varying number of doses before the performance of a repeat throat culture. The degree of positivity of the persistently positive cultures (1+, 2+, or 3+) was not shown.

Clinical performance and effect on treatment rates of latex agglutination testing for streptococcal pharyngitis in an emergency department.

Of 556 children with symptoms of streptococcal pharyngitis in a pediatric hospital emergency department, 38.8% had positive results on either a rapid latex agglutination test or throat culture for Group A Streptococcus. Twenty-six percent of patients with negative latex agglutination test results had growth on culture of a paired specimen. Under the best assumption rapid test sensitivity was 44.9%. The treatment rate (84%) for cases detected by the rapid test was markedly higher than the rate (44%) for cases detected only by culture (P less than 0.001), presumably because the rapid test result is available sooner. We conclude that: the rapid test had a lower sensitivity in routine use in our pediatric emergency department population than in previous reports from research settings; and using the rapid test in addition to culture can significantly increase treatment rates.

Low prevalence of Chlamydia trachomatis in the oropharynx of adolescents.

This study determined the prevalence rates of Chlamydia trachomatis infection in the oropharynx of adolescents with and without pharyngitis. One hundred teenagers with and without symptoms of pharyngitis were cultured for C. trachomatis. Swabs were taken from the oropharynx and tonsillar areas for direct fluorescent antibody assay and cell culture. Of the 100 adolescents enrolled in the study 55% had a history of pharyngitis and 45% had no pharyngeal symptoms; 29% were male and 71% were female. The mean age was 15.5 years. Forty-two percent had a history of sexual intercourse, and 11.5% described a history of oral-genital sex. Only one 14-year-old female with a 2-week history of a sore throat had a positive culture. Her direct fluorescent antibody assay was inconclusive and the throat culture for Group A Streptococcus was negative. She had no history of sexual activity. The overall prevalence rate in the 100 adolescents was 1% with a 1.8% prevalence in the symptomatic group and 0 in the asymptomatic group. Of the symptomatic adolescents 39 had cultures for Group A Streptococcus and 8 (20.5%) were positive. The results of this study suggest that C. trachomatis is a rare inhabitant of the oropharynx in adolescents and is not a common cause of pharyngitis.

Diagnosis and Treatment of Streptococcal Pharyngitis-Reply

Dr Soman's commentary on my editorial is appreciated. He raises a commonly recurrent question: should we stop use of penicillin, if once begun, if throat cultures for group A streptococci are negative? He cites three reports that show that infection is sometimes present and not detected by the throat culture techniques used. However, the clinician is left with an unsavory choice: should he continue using penicillin with no backup evidence for his clinical judgment, or should he discontinue its use, using the throat culture as an "absolute" gold standard? The answer is not easy. One balances the risk of unnecessarily prolonged exposure to penicillin (or an alternative antibiotic) against the risk of suppurative and/or nonsuppurative complications. The question and its resolution will have even greater implications as physicians abandon throat cultures for the rapid latex agglutination methods now being increasingly employed throughout the United States. Does a physician decide not to treat with penicillin initially if the result of the rapid test is negative? From the available sensitivity and specificity data and the clinical positive and negative predictive values, it appears

Throat cultures for group A beta-hemolytic Streptococcus. Importance of anaerobic incubation.

The bacteriologic detection of group A Streptococcus in pharyngitis is vital in everyday practice to prevent serious potential sequelae. The purposes of this study were to determine whether throat cultures should be incubated in anaerobic atmosphere and whether an increased recovery rate could be obtained by stabbing of the plates (partial anaerobiosis) and by using a sulfamethoxazole-trimethoprim disk to enhance growth and identification. We examined 243 throat cultures, in duplicate, which were incubated in room air and in anaerobiosis (carbon dioxide, 10%). We found that, in aerobic incubation, the recovery rate of group A streptococci was 5.7%; in anaerobic incubation it was 19.8%. Stabbing of the agar to create a partial anaerobiosis was useless. When directly placed on the plate, the sulfamethoxazole-trimethoprim disk facilitated the identification of beta-hemolysis areas. To achieve maximum detection of group A streptococci in specimens obtained from the throats of infected children, we found that anaerobic incubation should be used.

Beta-Hemolytic Streptococcal Pharyngitis

Infectious mononucleosis (IM) and beta-hemolytic streptococcal pharyngitis may present similar clinical pictures and may occur concurrently; however, recent studies have differed sharply with older ones that cited high rates of concurrent disease. Our study of 100 consecutive new patients meeting strict criteria for a diagnosis of IM found only 4% with positive throat cultures for group A beta-hemolytic streptococci at the time of diagnosis. Use of antibiotics for presumed streptococcal pharyngitis in patients with IM is unjustified. Only patients with positive cultures should be treated.

Upper Respiratory Tract Protocol

To the Editor. —The presentation of an upper-respiratory tract complaint protocol by Greenfield et al ( Arch Intern Med 133:294-299) and the result achieved with the use of this protocol were impressive from the standpoint of the organization of the data collection form and the decision-making algorithm; however, two additional interpretations of their results deserve mention. Although the statement is made that the protocol manifested equal or better judgement compared to the physicians, an examination of their results showed that, under the protocol's disposition, 22 patients would have received penicillin, seven of whom were shown to have positive throat cultures for group A β-hemolytic streptococci. This is a treatment accuracy of 32% as compared to the physicians' 25% accuracy, probably an insignificant difference. More important however, is the fact that the accuracy was only 32% and, taking into account that an additional four patients who did not receive penicillin under the