The diagnosis of strep throat in adults in the emergency room

Does this patient need to be evaluated today? Designing a guideline-driven triage process to determine the timing of care for adults with respiratory infection symptoms

BACKGROUND

Physicians and nurses often make judgments about the urgency with which patients require evaluation, yet few explicit process-of-care criteria are available to guide these decisions. Using a multidisciplinary expert physician panel and explicit, quantitative group judgment methods, standardized, clinically detailed deferred care criteria were developed to guide emergency department and ambulatory care triage decisions for same-day versus deferred care for patients with respiratory infection symptoms.

METHODS

Using a modified Delphi process, an eight-member multidisciplinary expert physician panel rated the safety of deferred care for standardized clinical scenarios. The ratings were converted into explicit criteria and then compared with usual implicit judgment in terms of nurse triage times.

RESULTS

The panel achieved 100% consensus on 36 critical clinical factors, each of which precludes deferring care for a patient with respiratory infection symptoms. Based on combinations of 12 additional clinical factors, 48 clinical scenarios were created that the panel rated for deferred care safety. Panelists' ratings agreed for 90% of clinical scenarios. These were formatted into screening criteria. Near-perfect interrater agreement (kappa = 0.9) was found in reproducibility testing. The difference in mean nurse triage times using the criteria compared with implicit nurse judgment was 0.4 minutes (95% confidence interval = -2.1 to 2.9 minutes).

CONCLUSIONS

Application of explicit criteria for deferring care of patients with respiratory infection symptoms did not lengthen triage time. This approach may facilitate more efficient resource management for ambulatory settings. However, widespread use before these criteria's, our systematic criteria-based triage should be validated in multicenter clinical trials against an outcome standard and the more common implicit approach.

Penicillin for acute sore throat: randomised double blind trial of seven days versus three days treatment or placebo in adults

OBJECTIVE

To assess whether treatment with penicillin for three days and the traditional treatment for seven days were equally as effective at accelerating resolution of symptoms in patients with sore throat compared with placebo.

DESIGN

Randomised double blind placebo controlled trial.

SETTING

43 family practices in the Netherlands.

PARTICIPANTS

561 patients, aged 15-60 years, with sore throat for less than seven days and at least three of the four Centor criteria-that is, history of fever, absence of cough, swollen tender anterior cervical lymph nodes, and tonsillar exudate. 142 patients were excluded for medical reasons and 73 needed penicillin.

INTERVENTIONS

Patients were randomly assigned to penicillin V for seven days, penicillin V for three days followed by placebo for four days, or placebo for seven days.

MAIN OUTCOME MEASURES

Resolution of symptoms in the first week, eradication of bacteria after two weeks, and recurrences of sore throat after two, four, and six months.

RESULTS

Symptoms resolved 1.9 and 1.7 days earlier in patients taking penicillin for seven days than in those taking penicillin for three days or placebo respectively. Symptoms resolved 2.5 days earlier in patients with group A streptococci and 1.3 days earlier in patients with high colony counts of non-group A streptococci. 23 (13%) of the placebo group had to be given antibiotics later in the week because of clinical deterioration; three developed a peritonsillar abscess. The eradication rate for group A streptococci was 72% in the seven day penicillin group, 41% in the three day penicillin group, and 7% in the placebo group. Sore throat recurred more often in the three day penicillin group than in the seven day penicillin or placebo groups.

CONCLUSION

Penicillin treatment for seven days was superior to treatment for three days or placebo in resolving symptoms of sore throat in patients with group A streptococcal pharyngitis and, possibly, in those with non-group A streptococcal pharyngitis.

Does clinical error contribute to unnecessary antibiotic use?

Patient expectations and physician attitudes are often cited as factors in the overuse of antibiotics. This study examined whether clinical error might also be important. In treating 517 patients with sore throat, family physicians estimated the probability that group A streptococcus infection was present. Two thirds of antibiotics prescribed were to culture-negative patients and therefore considered unnecessary. Physicians overestimated the probability that a group A streptococcal infection was present by an average 33.2% in these cases, compared with 6.9% otherwise (p < 0.001). The rate of unnecessary prescribing was 5.1% when the physician estimate differed from the true probability of a group A streptococcal infection by <10%, 16.0% for an error of 10-29%, 35.6% for an error of 30-49%, and 78.3% when the chance of the infection was overestimated by 50% or more. Clinical error in estimating the likelihood of group A streptococcal infection probably contributes to unnecessary antibiotic use in patients with sore throat.

Issues in the development, dissemination, and effect of an evidence-based guideline for managing sore throat in adults

BACKGROUND

In October 1995 the University of Michigan Healthcare System initiated a program to develop and implement guidelines for primary care in an effort to improve the quality and cost-effectiveness of care for common conditions associated with wide variations in clinical practice. One of these conditions was Group A beta-hemolytic streptococcus (GABHS), present in 5% to 20% of adults complaining of sore throat.

METHODS

A draft guideline was developed on the basis of a theoretical model of sore throat management, local data, and research evidence. The guideline was revised to reflect physicians' beliefs and practices regarding sore throat management. Guideline recommendations depended only on the number of clinical signs experienced by the patient and included testing only if it was likely to provide additional information about the probability of GABHS. Data on pre- and postdissemination data on patients presenting with sore throat were collected.

RESULTS

When physicians believed testing or antibiotics were unnecessary, only 7% of patients demanded screening and only 6% of patients wanted antibiotics. Physician beliefs about a patient's need for testing agreed with guideline recommendations in 63% of patients both before and after guideline dissemination.

DISCUSSION

Disseminating locally modified, evidence-based guidelines may not be sufficient to produce practice changes. If the guideline had been followed, the amount of testing would have been reduced by 17% and the appropriateness of testing improved for 32% of sore throat patients. The results indicate the need for implementation efforts that go beyond presenting evidence, even when that evidence is from both the literature and the local practice setting.

Evaluation of the patient with sore throat, earache, and sinusitis: an evidence based approach

Sore throat, earache, and sinusitis are common presenting complaints in the emergency department, and all fall within the top ten in the United States. These complaints usually have a benign course but rarely can be a symptom of a serious disease process. This article provides an evidence-based review of the literature regarding the diagnosis of pharyngitis, otitis media, and sinusitis.

Multivariate predictive models for group A beta-hemolytic streptococcal pharyngitis in children

OBJECTIVES

To create predictive models for the clinical diagnosis of group A beta-hemolytic streptococcal (GABHS) pharyngitis in children.

METHODS

Patients aged 6 months to 18 years presenting to a pediatric ED with suspected GABHS pharyngitis were prospectively enrolled in the study. Clinicians recorded pertinent clinical information using a standardized form and obtained a throat swab to culture GABHS using a reference standard method. Twelve demographic and clinical features of patients with positive throat cultures were compared with the features of patients with negative throat cultures. Significantly different features were entered in a stepwise logistic regression analysis to create predictive models for the diagnosis.

RESULTS

Eighty-five patients (29%) were culture-positive and 212 (71%) were culture-negative for GABHS. Respective mean ages were 6.2 years and 6.1 years in the two groups. Univariate chi-square analysis of the 12 features identified six variables that were significantly associated with GABHS. All significant features were initially included in a stepwise logistic regression analysis. In model I, four independent variables were identified: moderate to severe presentation of tonsillar swelling, moderate to severe tenderness and enlargement of cervical lymph nodes, the presence of scarlatiniform rash, and the absence of moderate to severe coryza, yielding a 95% probability for GABHS. Excluding the rare scarlatiniform rash, the remaining variables were used in the second regression analysis. In model II, three independent variables were identified: moderate to severe tonsillar swelling, moderate to severe tenderness and enlargement of cervical lymph nodes, and absence of moderate to severe coryza, yielding a probability of 65% for the diagnosis. A probability of <15% was observed in the absence of scarlatiniform rash, the absence of moderate to severe tenderness and enlargement of cervical lymph nodes, and the presence of moderate to severe coryza.

CONCLUSIONS

In children with moderate to severe presentation of tonsillar swelling, tenderness and enlargement of cervical lymph nodes, and the absence of coryza, the probability of a positive throat culture is >65%. Conversely, in the absence of a moderate to severe presentation of tonsillar swelling, enlargement of cervical nodes, and the presence of coryza, the probability of a positive throat culture is <15%. If prospectively validated, these models could be integrated into a consistent treat, test, and no treatment/no testing approach to the clinical management of childhood pharyngitis.

Determination of Class II and Class III skeletal patterns: receiver operating characteristic (ROC) analysis on various cephalometric measurements

Receiver operating characteristic analysis is an excellent method for evaluating and comparing the performance of diagnostic tests. The purpose of this study was to use the receiver operating characteristic analysis to evaluate the diagnostic ability of several cephalometric measurements in determining the presence of Class II and Class III skeletal patterns. Receiver operating characteristic analysis was performed on 976 cases. Fifteen cephalometric measurements were evaluated. A computer software program ROC ANALYZER was used to tabulate the areas under the curves and to perform the statistical comparison between the curves. The results of this study indicated that the Anteroposterior Dysplasia Indicator had the best diagnostic ability in identifying cases with Class II and Class III skeletal patterns. WITS Appraisal and Overjet were highly effective in diagnosing cases with Class II skeletal pattern. WITS Appraisal, Convexity, AB Plane Angle and Overjet also performed well in diagnosing cases with Class III skeletal pattern.

Effect of an explicit decision-support tool on decisions to prescribe antibiotics for sore throat

Studies of scoring rules for sore throat have failed to show that they lower antibiotic prescription rates. The authors studied the effect of an explicit decision-support tool, incorporating a modified score, on antibiotic-prescription decisions. Four hundred and fifty family physicians received an information package, a score card, and a recording form to use during one sore-throat encounter. The physicians randomly received either a control form or an intervention form that required them to interact with the score during the clinical recording process. There was a trend towards a reduction in antibiotic prescriptions (21%, p=0.09) in the physicians using the intervention form. A greater reduction (45%, p=0.06) was observed for patients whose probabilities of infection with group A streptococcus were low. Sore-throat-scoring rules may reduce unnecessary antibiotic prescriptions if physicians are specifically cued to use them during clinical encounters and appropriate management responses are linked to score estimates for the likelihood of group A streptococcus infection.

Food-borne and air-borne streptococcal pharyngitis--a clinical comparison

Different vehicles of transmission of the same pathogen may induce different clinical manifestations of the disease. The hypothesis was tested that the clinical manifestation of food-borne streptococcal pharyngitis is different from air-borne streptococcal pharyngitis. The symptoms and signs of 77 patients with endemic air-borne streptococcal pharyngitis compared to 103 patients with epidemic food-borne streptococcal pharyngitis (T type 8/25/imp19, M protein negative) and 11 patients with secondary air-borne epidemic streptococcal pharyngitis (T type 8/25/imp19, M protein negative) were prospectively evaluated. The patients with food-borne streptococcal pharyngitis had a significantly higher frequency of sore throat, fever, pharyngeal erythema, tonsillar enlargement and submandibular lymphadenopathy and a lower frequency of coryza and cough compared to the patients with endemic air-borne streptococcal pharyngitis. Although both food-borne and air-borne streptococcal infection caused upper respiratory tract infection, the clinical manifestation of food-borne streptococcal pharyngitis was more severe and more confined to the pharynx compared to the endemic air-borne disease. Involvement of the nasal mucosa and bronchial tree was more common in air-borne streptococcal pharyngitis than in the food-borne disease.

Should nurses in Israeli primary care clinics be expected to manage streptococcal throat infections?

INTRODUCTION

Legal regulations in Israel allow nurses to perform only limited clinical procedures.

OBJECTIVE

To determine the probability of streptococcal infection in adults with sore throat, as assessed clinically by standard nursing procedures.

DESIGN

Using throat culture as the standard, the contribution of various clinical findings (fever, exudate, erythrocyte sedimentation rate (ESR), white blood count) to the determination of the diagnosis of streptococcal infection was assessed, using logistic regression analysis.

SETTING

Israeli general practice.

PATIENTS

100 consecutive adult patients presenting with a red, sore throat.

RESULTS

Six patients showed the full clinical picture of exudate, increased ESR and leukocytosis, with an 82% probability of streptococcal infection. Forty-nine patients showed none of these three findings, and only one of them (among the three patients with rhinitis) had a positive throat swab. Forty-five patients showed an intermediate clinical picture which did not provide a reliable basis for the diagnosis or exclusion of streptococcal infection. Fever alone did not significantly (P < 0.05) predict streptococcal infection.

CONCLUSIONS

Nurses may safely discharge adult patients with a red, sore throat without antibiotic treatment only if they have no additional signs or symptoms. The few patients with all the clinical findings may be treated with antibiotics without a throat swab. All other patients should be referred for examination by a doctor.

Accuracy of anticardiolipin antibodies in identifying a history of thrombosis among patients with systemic lupus erythematosus

OBJECTIVE

To measure the accuracy of anticardiolipin antibodies (aCL) in identifying a history of thrombosis among patients with systemic lupus erythematosus (SLE) or the primary antiphospholipid syndrome (PAPS).

PATIENTS AND METHODS

Patients with SLE or PAPS who attended our rheumatology clinic between April 1992 and March 1994 were included in a retrospective analysis of the relationship between thrombotic events and aCL. All aCL measurements were performed in the same laboratory by enzyme-linked immunosorbent assay, blinded as to the presence or absence of thrombosis. The diagnostic accuracy of IgG, IgM, and IgA aCL was quantified by means of the receiver operating characteristic area under the curve (ROC AUC) for each isotype. Stratum-specific likelihood ratios and their 95% confidence intervals were calculated to define strata with optimal discriminant power.

RESULTS

During the period of study, aCL was measured in 117 patients (113 SLE and 4 PAPS), of whom 24 (20.5%) had experienced thrombotic events. The ROC AUC +/- the standard error for IgG aCL was 0.81 +/- 0.05, signifying an 81% accuracy in the identification of a history of thrombosis. In contrast, the accuracy of the IgM and IgA aCL was significantly lower (0.60 +/- 0.08 and 0.54 +/- 0.07, respectively, P < 0.05). Using stratum-specific likelihood ratios, we defined three strata in the IgG aCL scale that discriminate between patients with low, indeterminate, and high probabilities of thrombosis. For IgG aCL levels below 21.4 IgG phospholipid (GPL) U/mL, the posttest probability of thrombosis was 0.07, whereas for IgG aCL levels > or = 65.1 GPL U/mL, the posttest probability of thrombosis was 0.75. For IgG aCL values between 21.4 and 65.0 GPL U/mL, the probability of thrombosis was 0.20, equivalent to the entire cohort.

CONCLUSIONS

The IgG aCL determinations perform well in the identification of thrombosis in SLE or PAPS, while the IgM and IgA aCL have poor diagnostic accuracy. These findings may have implications for management of these patients.

You can lead a horse to water--improving physicians' knowledge of probabilities may not affect their decisions

OBJECTIVES

To determine whether improving physicians' judgments of the probability of streptococcal pharyngitis for patients with sore throats would affect their use of antibiotics and affect the variation in such use.

DESIGN

Post-hoc retrospective analysis of data previously collected as part of a controlled trial.

SETTINGS

University student health services in Pennsylvania and Nebraska.

PATIENTS

Sequential patients with pharyngitis seen before and after the time clinicians received either an experimental educational intervention designed to improve probabilistic diagnostic judgments (at the Pennsylvania site) or a control intervention, a standard lecture (at the Nebraska site). The clinician-subjects were the primary case physicians practicing at either site.

MEASUREMENTS

Clinical variables prospectively recorded by the clinicians, probability assessments, and treatment decisions.

RESULTS

At the experimental site, despite marked decreases in clinicians' overestimations of disease probability after the intervention, the proportion of patients prescribed antibiotics showed a trend toward increasing: 100/290 (34.5%) pre-intervention, 90/225 (40%) post-intervention. The intervention did not decrease practice variation between individual doctors. Univariable and multivariable analyses showed no major change in the relationships between clinical variables and treatment decisions after the intervention. At the control site there was no major change in probability judgments or treatment decisions after the intervention.

CONCLUSIONS

Teaching physicians to make better judgments of disease probability may not alter their treatment decisions.

Streptococcal pharyngitis: a review of pathophysiology, diagnosis, and management

Pharyngitis is an illness frequently treated by emergency physicians and primary care practitioners. It is the subject of much controversy regarding optimal treatment in the acute care setting. This review discusses pertinent aspects of the pathophysiology, clinical features, diagnosis, and treatment based on available literature. This review is also meant to serve as a bibliographic resource for some of the controversies of this complex topic.

Practice variation in the management of pharyngitis: the importance of variability in patients' clinical characteristics and in physicians' responses to them

The objective of this study was to assess whether geographic differences in antibiotic-prescribing rates for patients with pharyngitis could be explained by intersite differences in patients' clinical characteristics and in how physicians responded to these clinical cues when making decisions. As part of the initial phase of a prospective controlled trial to improve physicians' diagnostic ability, the authors enrolled cohorts of consecutive patients seen at staff-model--HMO student health services in Pennsylvania and Nebraska. Physicians' decisions whether to prescribe antibiotics for 310 consecutive patients presenting with pharyngitis to the former and 214 such patients presenting to the latter at the time of the initial visit were examined. There was a large discrepancy between the antibiotic-prescribing rates at the student health services in Pennsylvania, 106/310, 32.4%, and Nebraska, 156/214, 72.9%. The clinical variables significantly independently associated with treatment at both sites in a logistic regression model were fever, adjusted odds ratio = 2.1 (95% CI = 1.1, 3.8); exudates, 5.4 (2.8, 10); palatine petechiae, 6.5 (1.5, 28); rhinorrhea, 0.46, (0.25, 0.85); and high risk of complications, 3.8 (1.04, 14). There was a significant interaction between site and anterior cervical adenopathy, 5.5 (1.6, 19); and a borderline interaction between site and rhinorrhea, 2.4 (0.89, 6.7). Site was not a significant independent predictor of treatment, 1.8 (0.45, 6.6.). Practice variation was related to geographic differences in patients' clinical characteristics and in how physicians responded to these factors when prescribing antibiotics. How physicians weight patients' clinical characteristics when making decisions may be an important element of their "practice styles."

Integrating stratum-specific likelihood ratios with the analysis of ROC curves

Data used to construct receiver operating characteristic (ROC) curves and to calculate the area under the curve (ROC AUC) can be used to derive stratum-specific likelihood ratios (SSLRs) with their 95% confidence intervals (95% CIs). The purpose of this study was to determine whether useful information can be obtained by adding SSLRs to the analysis of ROC curves. The authors analyzed four previously reported sets of data: 1) serum creatine kinase (SCK) for diagnosing acute myocardial infarction (AMI) in the coronary care unit (CCU); 2) SCK in the evaluation of chest pain in the emergency center (EC); 3) four predictor variables in the diagnosis of strep throat; and 4) the ordinal assessment of computed tomographic (CT) images. Use of SCK in the CCU produced four strata that had posttest probabilities that were highly discriminating, whereas SCK in the EC resulted in only two strata with limited discriminating ability. In either study the cutpoint at which the SSLR changed from less than to greater than 1.0 was higher than the reported upper normal for the test, thereby quantitating spectrum bias. The maximum number of strata of predictor signs and symptoms for strep throat was three rather than the five used in previous studies. With a larger sample size or pooling, four strata could probably be developed. With CT images, "definitely normal," "probably normal," and "questionable" were collapsed to one negative stratum. "Probably abnormal" became the true "questionable" stratum and "definitely abnormal" was the only positive stratum. The authors conclude that additional useful information is obtained by deriving stratum-specific likelihood ratios as part of the analysis of an ROC curve.

Using treatment-tradeoff preferences to select diagnostic strategies: linking the ROC curve to threshold analysis

Selection of optimal diagnostic strategies depends on the accuracy of diagnostic tests, the prevalence of disease, and the relative benefits and harms resulting from test/treatment choices. One can characterize diagnostic strategies according to their net benefit-to-harm ratios. Within the framework of expected-utility theory, the benefit-to-harm ratio is equivalent to the marginal tradeoff between erroneous and correct treatment choices. Consequently, a physician can identify his or her preferred strategy by asking the question: "How many additional treatment errors am I willing to make in order to treat one additional person correctly?" Family physicians were asked to indicate their lowest and highest acceptable tradeoff ratios in a survey about streptococcal pharyngitis. All 53 respondents indicated uncertainty about their preferred treatment-tradeoff ratios. For 58% of respondents, the midpoints of the acceptable range of tradeoff ratios corresponded to generally accepted diagnostic strategies: 1) test all or 2) treat if classic, test all others. In contrast, previously published patient utilities yield a treatment-tradeoff ratio that corresponds to the strategy of treating all cases. The analysis illustrates the linkage between the optimal operating point on a receiver operating characteristic (ROC) curve and the selection of a preferred diagnostic strategy based on treatment thresholds derived from benefit-to-harm ratios. The survey results indicate that physicians can respond directly to questions assessing their preferences for such treatment thresholds. Differences between patients and physicians have significant impacts on choices of test and treatment strategies.

Assessment of clinical features predicting streptococcal pharyngitis

A total of 133 patients who consulted 4 general practitioners in Bergen 1988/89 for sore throat were examined. 8 clinical parameters with expected predictive value for identifying streptococcal tonsillopharyngitis were recorded. Clinical examination was validated against bacteriologic examination at a microbiological laboratory. The prevalence of streptococcal infection (group A, C and G) was 29%. An algorithm was constructed which identifies 3 groups with varying probabilities of streptococcal infection. A positive predictive value of 62% in the group with highest prevalence and a negative predictive value of 90% in the group with lowest prevalence was found. The consequences of performing a confirmative test only on patients in the group with uncertain prediction for streptococcal disease was elaborated. Although slightly reduced accuracy was demonstrated, due to diminished sensitivity, selective testing is recommended. Another algorithm was constructed for use in situations where no confirmative testing is available. The positive predictive value in the group with highest probability of streptococcal infection was 51%, and the negative predictive value in the group with lowest probability was 84%.

An algorithm for a selective use of throat swabs in the diagnosis of group A streptococcal pharyngo-tonsillitis in general practice

A prospective evaluation was made of an algorithm for a selective use of throat swabs in patients with sore throat in general practice. The algorithm states that a throat swab should be obtained (a) in all children younger than 15 years; (b) in patients aged 15 years or more who have pain on swallowing and at least three of four signs (enlarged or hyperaemic tonsils; exudate; enlarged or tender angular lymph nodes; and a temperature > or = 38 degrees C); and (c) in adults aged 15-44 years with pain on swallowing and one or two of the four signs, but not both cough and coryza. Group A streptococci were found by laboratory culture in 30% of throat swabs from 1783 patients. Using these results as the reference, the algorithm was 95% sensitive and 26% specific, and assigned 80% of the patients to be swabbed. Its positive and negative predictive values in this setting were 36% and 92%, respectively. It is concluded that this algorithm may be useful in general practice.

Diagnosis of pneumonia in adults in general practice. Relative importance of typical symptoms and abnormal chest signs evaluated against a radiographic reference standard

The diagnostic value of typical symptoms and abnormal chest signs for pneumonia have been evaluated against a radiographic reference standard in 402 adult patients with respiratory tract infection in general practice. Pneumonia was diagnosed in 20 patients by a positive chest radiograph. The doctors diagnosed pneumonia in seven of these on the basis of history and physical examination alone, and in addition in 22 patients with normal radiographs. The diagnostic value of the typical symptoms cough, chest pain, and dyspnoea, reported by the patients on a questionnaire, increased with increasing intensity of the symptoms, and both "very annoying lateral chest pain" and "very annoying dyspnoea" had likelihood ratios (LR) between 4 and 5. The LR of crackles was 3.7. When evaluated against the doctor's clinical diagnosis of pneumonia as reference standard, crackles achieved an LR of 14.8, while the typical symptoms achieved lower LRs than when evaluated against the radiographic reference standard. These discrepancies, which were confirmed by logistic regression, indicate that crackles and other abnormal chest findings are interpreted too frequently as features of pneumonia and that the importance of typical symptoms is underestimated in the diagnosis of pneumonia.

Confidence intervals for post-test probability

Confidence intervals are a natural way to describe the uncertainty of post-test probability in diagnostic tests. We consider confidence intervals for two different scenarios. At a site, for example, hospital emergency room or student health centre, with measured values of disease prevalence, sensitivity and specificity available, the confidence interval is similar to results in the literature, but at a site where measured values of these indices are unavailable, we develop a method, using the values of disease prevalence, sensitivity and specificity from other sites, to obtain a confidence interval for post-test probability. We use the diagnosis of strep throat to illustrate the results. We also obtain confidence intervals from simulations to compare with the results of both scenarios.

Monocytes and polymorphonuclear neutrophils of patients with streptococcal pharyngitis express increased numbers of type I IgG Fc receptors

Studies using cultured cells have shown that gamma interferon (IFN-gamma) induces the expression of Fc gamma RI (the type I Fc receptor for IgG) on human polymorphonuclear neutrophils (PMN) and greatly increases the number of these receptors on human monocytes. Administration of rIFN-gamma in vivo also causes enhanced Fc gamma RI expression on these cell populations. Because streptococcal antigens are potent inducers of IFN-gamma in vitro, we postulated that IFN-gamma would be produced endogenously in vivo in patients with streptococcal infections. Such production of IFN-gamma in vivo, even at low levels, might be expected to induce the expression of Fc gamma RI on monocytes and neutrophils. To evaluate this possibility, we used monoclonal antibody 32 (mAb 32), which is specific for Fc gamma RI, to quantitate the expression of this receptor on human peripheral blood cells. We measured the binding of mAb 32 to monocytes and PMNs isolated from healthy donors and from patients with group A beta-hemolytic streptococcal (GABHS) pharyngitis. PMNs from healthy donors (n = 12) had 700 +/- 600 (mean +/- SD) mAb 32 binding sites. Patients with pharyngitis and negative throat culture for GABHS (n = 11) had 2,100 +/- 1,600 sites on their PMNs. In contrast, the PMNs from patients with documented GABHS pharyngitis (n = 12) had 11,600 +/- 7,500 mAb 32 binding sites on their surface. There was a similar change in the expression of Fc gamma RI on monocytes, with control monocytes having a mean of 19,900 +/- 3,200 mAb 32 binding sites per cell and the GABHS-positive monocytes having 47,500 +/- 21,400 sites. The GABHS-negative throat culture group had a slightly elevated number of Fc gamma RI with a mean of 28,200 +/- 8,400 sites. 10 patients with documented urinary tract infections and three patients with uncomplicated pyelonephritis had no elevation in Fc gamma RI expression. These studies demonstrate that a localized group A streptococcal infection can cause systemic activation of the entire circulating pool of phagocytes, and suggest that a similar level of activation is uncommon in localized gram-negative infections of the urinary tract.

Use of linear models to analyze physicians' decisions

Linear models of judgment are powerful tools for studying medical decision making. The recent increase in applications of these models to medicine reflects more available computing resources and the parallel development of clinical prediction rules derived from multivariate analysis of patient data. Psychological research into expert and novice decision making shows that linear models derived from judges' decisions usually predict future decisions more accurately than either the judge or a mechanical application of the judge's stated policies. Studies of medical decision making have shown similar results, as well as marked variation among experts in how they appear to use clinical information. Cognitive feedback, which is feedback to the learner of the judgment model derived from previous decisions, is highly effective for teaching complex judgment tasks. Many technical problems remain to be mastered in constructing linear models of medical judgment. These include how to select the correct variables, how to provide a selection of variables broad enough to accommodate individual variations in strategy, how to model intercorrelated variables, and how to characterize and aggregate individual strategies. Despite the methodologic challenges, linear models remain a powerful method for studying how physicians combine multiple items of imperfect information to make a judgment. These techniques may provide important insights into variation in physician judgments. In addition, they hold promise in teaching the appropriate integration of complex data in the day-to-day practice of medicine.

Rational decision making based on history: adult sore throats

Primary care physicians are often required to make preliminary evaluations based only on the patient's history, especially during telephone encounters about sore throats. The authors studied adults with sore throats to determine whether patients can be stratified into higher and lower risks of strep throat by history alone. They first obtained data from 517 patients seen in an emergency room. Providers graded symptoms on a four-point scale (absent, mild, moderate, or severe). Initial analyses showed that prediction based on history should include three variables: fever, difficulty in swallowing, and cough. For ease of computation, these were consolidated into one score, "history" (= fever history + difficulty in swallowing - cough). This score was used to develop a model that predicts the probability of infection with group A beta-hemolytic streptococcus, and the model's performance was tested in two additional patient groups. The predictive accuracy of the "history" score was confirmed in all patient groups, despite differences in providers and disease prevalences. Primary care physicians may use this model to help them make decisions in situations such as telephone encounters without using additional data.

Variability in physician estimates of survival for acute respiratory failure in chronic obstructive pulmonary disease

Physician estimates of patient survival often influence clinical decisions. I studied physician estimates of survival for a patient with acute respiratory failure and underlying chronic obstructive pulmonary disease to identify the factors that may influence these estimates. Physicians (n = 205) completed the same patient management problem and estimated the length of survival for the hypothetical patient. Physician estimates of survival were quite variable, ranging from one month to five years. Shorter estimates of survival were associated with acquisition of select case information: subjective information from family members and a professional colleague, and physiologic and functional data previously demonstrated to be predictive of survival. The study suggests that estimates of survival for the same patient may vary among physicians because of different considerations of social and physiologic case information. Physician estimates of patient survival and treatment recommendations may become more uniform with additional education or decision aids regarding the prognostication of survival.

Teaching medical students to estimate probability of coronary artery disease

The authors conducted a randomized trial of two methods for teaching medical students how to estimate the probability of coronary artery disease in patients with chest pain. Eighty-two students were given a pre-test consisting of written protocols summarizing the histories of 25 patients who had undergone coronary arteriography. The students estimated the likelihood of coronary artery disease for each case and were then randomized to receive one of two short written clinical lessons: a cardiology textbook chapter on interpreting chest pain, or a lesson based on a prediction rule for estimating probability of coronary artery disease. All students were given a post-test similar to the pre-test. Students who were given the textbook lesson showed no change in the accuracy of their probability estimates. Students who were taught the prediction rule significantly improved their probability estimates, as measured by a statistical index of calibration. The authors conclude that traditional teaching methods do not provide students with guidance in estimating disease probability, and that better teaching methods are needed. In this study, a clinical prediction rule fulfilled the need for instruction in probability estimation.

Rapid diagnosis of streptococcal pharyngitis in adult emergency room patients

A rapid latex agglutination slide test for group A beta-hemolytic streptococcal throat infections was prospectively evaluated. Resident physicians, working in an adult non-acute emergency room, recorded clinical data and collected throat swabs from 729 adult patients with sore throats. Research assistants obtained throat swabs from 329 control patients. Sensitivity and specificity, compared with routine cultures, were 96% and 97%, respectively. Analyses of clinical predictions and of test results for control patients, however, suggest that this test may perform better than routine culture. The test provides a rapid, accurate, potentially useful alternative for diagnosing group A beta-hemolytic streptococcal pharyngitis in adults.

The prediction of streptococcal pharyngitis in adults

The usefulness of clinical and laboratory findings for prediction of the presence of Group A streptococci on throat culture and of an increase in antistreptococcal antibodies was investigated in 693 adult patients. Several findings were shown to increase the likelihood of streptococcal isolation, alone and in combination: tonsillar exudate, tonsillar enlargement, tender anterior cervical adenopathy, myalgias, and a positive throat culture in the preceding year. Compared with a frequency of 9.7% in all patients, the probabilities of a positive culture were quite different (ranging from 2 to 53%) in subgroups of patients with different combinations of these clinical findings. The results of a leukocyte count and measurement of C-reactive protein added little additional predictive information. While clinical findings can never predict perfectly the results of a throat culture, they nevertheless can provide useful information--particularly in tending to "rule out" streptococcal infection--in adult patients with pharyngitis.

A Visicalc program for estimating the area under a receiver operating characteristic (ROC) curve

The area under the ROC curve interests us as a method for analyzing discrimination or detectability. One can assess a diagnostic test or probability assessor with respect to its degree of discrimination. The area under the ROC curve gives us the probability of correctly identifying abnormal from normal in a forced-choice, two-alternative problem. Previous methods used for calculating the area involved maximum likelihood estimation on a mainframe or minicomputer. This paper demonstrates an adaptation of a recently published nonparametric method for estimating the area. This adaptation takes advantage of electronic spreadsheet software and may be used on most (if not all) microcomputers. The paper develops the construction of the program needed for the necessary calculations.

A differential diagnostic approach to the symptomatology of acute dental pain

Seventy-four patients with acute pulpitis, apical periodontitis, marginal periodontitis, or pulpoperiodontitis were examined. A series of symptoms and signs was registered. Diagnostic specificities and sensitivities were calculated, and thirteen variables were subjected to discriminant analysis and log-linear multiway contingency table analysis. Pulpoperiodonitis was found inseparable from pulpitis on the basis of the registered symptoms and signs. Several symptoms and signs previously believed to have differential diagnostic power were found insignificant. The following combination of symptoms and signs yielded a correct diagnosis in 82.1% of the cases: constant pain, tenderness to temperature changes, "the tooth feels extruded," impaired mouth opening, tenderness to palpation in apical area, and mobility.

Pharyngeal infections. Causes, findings, and management

Pharyngitis is one of the most common clinical problems. Its causes are multiple, two of the best known being streptococcal infection and infectious mononucleosis. Group A beta-hemolytic streptococcal infections are the focus of diagnostic and therapeutic efforts aimed at reducing the risk of both suppurative and nonsuppurative complications. Several non-group A infections are important to recognize as sources of pharyngitis. In addition, mycoplasmal and chlamydial pharyngitis may be more prevalent than is realized. The possibility of gonococcal pharyngitis should be given special attention because of the severity of complications. Recurrent pharyngitis is difficult to manage. Except for certain specific indications, tonsillectomy remains an unproven therapeutic approach.

Treating sore throats in the emergency room. The importance of follow-up in decision making

Evaluation and treatment of emergency room patients complaining of sore throats are complicated by an unknown probability of follow-up. Tompkins' analysis of cost-effective sore throat management strategies was modified by adding an expression for variable follow-up rate. The original analysis specified a culture range when the probability of streptococcal infection was between 0.05 and 0.20, while the expanded analysis demonstrates that this range decreases with decreasing follow-up. For follow-up rates of 0.70 or less, all patients would be in either the treatment or no treatment group. This analysis demonstrates the importance of follow-up in out-patient decision making, and illustrates the methodology for including follow-up (and similar factors) in our analyses.