Strep Throat RCE


Does This Patient Have Strep Throat?

Original Citation: Ebell et al. Does this patient have strep throat? JAMA, 2000:284:2912-2918.

Reviewed by: Valenica Eggleston-Clark, MD Date: August 2005

Bottom Line

•A single element in history and physical is not enough to confirm probability of strep throat

•Physicians should adopt a set of clinical prediction rules to determine whether rapid antigen test or culture is warranted to diagnose strep throat.

•Establishment of prediction rules can help physicians prevent increasing health care costs by avoiding culture and/or rapid antigen testing with every patient that presents with complaints of sore throat. Strep throat can be established by dividing patients into low, moderate or high risk.

SORT Grade of Recommendation: A, based on consistent good quality evidence

Updated Search Findings The use of clinical prediction rules (Centor and McIsaac) to diagnosis strep pharyngitis have high specificity for agreement with physicians’ judgment that patients did not have strep throat. Level 2

Comments/Hints/Suggestions

Prevalence:

Pharyngitis can have several etiologies, however, the probability of streptococcal pharyngitis is 5-36%, which is second only to viral etiologies.

Asymptomatic carrier rates are as follows: 5-20% in children ages 3-15, 1.9-7.1% in children younger than three, 2.4-3.7% in adolescents (<15) and adults.

Accuracy of Exam

Symptoms

Positive LR

Negative LR

Any exudates

1.5-2.6

0.66-0.94

Reported fever

0.97-2.6

0.32-1.0

Measured temperature >37.8C

1.1-3.0

0.27-0.94

Anterior cervical nodes swollen/enlarged

0.47-2.9

0.58-0.92

Pharyngeal exudates

2.1 (1.4-3.1)

0.90 (0.75-1.1)

Tonsillar swelling/enlargement

1.4-3.1

0.63 (0.56-0.72)

Signs

Tonsillar or pharyngeal exudates

1.8 (1.5-2.3)

0.74 (0.66-0.82)

Anterior cervical nodes tender

1.2-1.9

0.600.49-0.71)

Tonsillar exudates

3.4 (1.8-6.0)

0.72 (0.60-0.88)

No cough

1.1-1.7

0.53-0.89

No coryza

0.86-1.6

0.51-1.4

Myalgias

1.4 (1.1-1.7)

0.93 (0.86-1.0)

History of sore throat

1.0-1.1

0.55-1.2

Headache

0.81-2.6

0.55-1.1

Pharynx injected

0.66-1.63

0.18-6.42

Measured temperature 38.3C

0.68-3.9

0.54-1.3

Nausea

0.76-3.1

0.91-(0.86-0.97)

Duration < 3 d

0.72-3.5

0.15-2.2

Male sex

0.87 (0.72-1.05)

1.1 (0.93-1.2)

Palatine petechiae

1.4 (0.48-3.1)

0.98 (0.92-1.1)

Strep exposure previous 2 wk

1.9 (1.3-2.8)

0.92 (0.86-0.99)

Rash

0.06-35

0.90-1.1

Description of how symptoms elicited or defined

Description of how exams were done or of prediction rules

Centor Clinical Prediction Rule

1. Assign 1 point for each of the following clinical characteristics: (1) history of fever, (2) anterior cervical adenopathy, (3) tonsillar exudate, and (4) absence of cough.

2. Find the column that most closely matches the pretest probability of strep in the patient and look down the column to the row that matches the patient’s number of points to determine the probability of strep.

Pretest Probability

Points, no.

LR

5

10

15

20

25

40

50

0

0.16

1

2

2

3

5

10

14

1

0.3

2

3

5

7

9

17

23

2

0.75

4

8

12

16

20

33

43

3

2.1

10

19

27

34

41

58

68

4

6.3

25

41

53

61

68

81

86

McIsaac Modification of the Centor Strep Score

1. Add up point for Patient

Symptoms or Sign

Points

History of Fever or Measured Temp >38C/100.4F

1

Absence of Cough

1

Tender Anterior Cervical Adenopathy

1

Tonsillar Swelling or Exudates

1

Age < 15 y

1

Age > 15 y

-1

2. Find Risk of Strep

Points

LR

% With Strep

-1 or 0

0.05

1

1

0.52

10

2

0.95

17

3

2.5

35

4 or 5

4.9

51

Precision:

Kappa test was not used to evaluate precision. Although data was limited, observer agreement (i.e. examination of ears, nose, throat, cervical nodes and chest) was found to be 88%, suggesting high observer reliability.

Studies description

Inclusion criteria: Studies that specifically examined signs/symptoms relevant to the diagnosis of strep throat in patients complaining of sour throat. Studies that included at least 300 patients, and used throat culture as gold standard.

Search Date: MEDLINE

Number Found and Reviewed: 917 articles found that studied patients complaining of sore throat. Inclusion criteria were the following: at least 300 patients in study, collected data prospectively, used throat culture as the reference standard. 17 studies met all of the inclusion criteria except size. Nine studies included 300 patients.

Quality/Limitations:

Gold Standards: Throat culture was the reference standard to determine diagnosis of strep pharyngitis.

Quality: All articles were considered Level 1 defined as prospective data, study included at least 300 patients, and examiners were blind to rapid antigen test and culture results.

Unpublished data on the diagnosis of strep pharyngitis was not sought.

Dates for MEDLINE search were not given. No other databases were searched.

Several clinical prediction rules were given for the prediction of strep throat in both adult and pediatric patients with sore throat.

Limitations: Limited data included in studies regarding precision of symptoms and signs.

Updated SearchDate: August 2005

Article: Pharyngitis clinical prediction rules: effect of interobserver agreement. Journal of Clinical Epidemiology. 2004:57:142-146

Description: This cross-sectional study assessed clinician variabliltiy in assessing pharyngitis using clnical prediction rules. The Centor and McIsaac clinical prediction rules for strep phyrngitis were used to determine how physician agreement affected sensitivity, specificity and projected rates of antibiotic prescribing and praid antigen testing. The Agree Group (physicians who agreen on all four Centor criteria) were compared to the Disagreed Group (physicians were disagreed on one or more criteria).

Findings:

Measurements of clinician agreement on sore throat H&P examination elements

Assessment Variable

N

Po

Pe

K

History of cough

161

0.86

0.55

0.70

History of fever

160

0.78

0.52

0.53

Patient appears flushed

196

0.80

0.71

0.31

Tonsillar exudate

193

0.88

0.75

0.52

Pharyngeal erythema

193

0.73

0.68

0.17

Posterior pharyngeal exudate

195

0.89

0.75

0.21

Enlarged anterior cervical nodes

197

0.60

0.51

0.20

Tender anterior cervical nodes

197

0.74

0.54

0.44

Enlarges posterior cervical nodes

196

0.90

0.90

0.05

Tender posterior cervical nodes

196

0.91

0.91

0.06

Bold = components of Centor and McIsaac clinical prediction rule

N = # of sore throat patients with sign/symptom

Po = Observed agreement

Pe = Agreement expected by chance

K = Kappa coefficient

Results of application of Centor clinical prediction rule to Agreed and Disagreed groups

Agreed Group (N=80)

Disagreed Group (N=77)

Sensitivity

75.0% (6/8)

70.0% (7/10)

Specificity

98.6% (71/72)

98.5% (66/67)

Hypothetic rapid antigen test

32.5% (26/80)

53.2% (41/77)

Hypothetic antibiotic prescription

8.8% (7/80)

10.4% (8/77)

Results of application of McIsaac clinical prediction rule to Agree and Disagreed groups

Agreed Group (N=82)

Disagree Group (N=63)

Sensitivity

75% (6/8)

75% (6/8)

Specificity

98.6% (73/74)

96.4% (53/55)

Hypothetic rapid antigen test

29.3% (24/82)

50.8% (32/63)

Hypothetic antibiotic prescription

8.5% (7/82)

12.7% (8/63)

Critique: Study included a small sample size (N=200). Only adults were included in the study. The study was conducted in an academic setting, which was not characteristic of all clinical settings. The study allowed level II and III residents to perform H&P, in which one could question their examination skills as compared to the attendings who also participated in the study.

Level of Evidence: Level 2 due to: small sample size, adult only patient population.

Fit: This study showed that the use of clinical prediction rules (Centor and McIsaac) to diagnosis strep pharyngitis have high specificity for agreement with physicians’ judgment that patients did not have strep throat. This, in theory, decreases the use of rapid antigen testing and unnecessary antibiotic prescribing. Without use of clinic prediction rules there is only moderated agreement among physicians on key H&P components that determine rapid antigen testing and antibiotic prescribing. This was a similar finding in the rational clinical exam study.

Reviewed by: Valenica Eggleston-Clarke MD Todd McDiarmid MD Date Aug 2005


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