Strep Throat
Released: Aug 1, 2018
Does Your Patient Have Streptococcal Pharyngitis? No Problem -- I'll just Swab. Not So Fast...
Fagan Nomogram for Likelihood Ratios
1. Decide on your pre-test probability of the disease (choose an approximate probability based on our assessment)
2. Use the likelihood ratio that correlates to your exam.
3. Draw a straight line frm your pre-test probability starting point, to the LR of the feauture/test, take it through to find your post-test probability
4. Use this new post-test probability to help in your decision
Your patient has palatal petechiae, which confers a positive likelihood ratio (LR+) of 2.7
See below how to use this statistic based on your clinical assessment"
Low Probability
Moderate Probability
High Probability
List of Likelihood Ratios for Streptococcal Pharyngitis Symptoms and signs Positive LR (95% CI) Negative LR (95% CI) Sensitivity (95% CI) Specificity (95% CI) Scarlatiniform rash 3.91 (2.00-7.62) 0.94 (0.90-0.97) 0.08 (0.05-0.14) 0.98 (0.95-0.99) Palatal petechiae 2.69 (1.92-3.77) 0.90 (0.86-0.94) 0.15 (0.10-0.21) 0.95 (0.91-0.97) Chills 2.16 (0.94-4.96) 0.88 (0.79-0.98) 0.21 (0.18-0.24) 0.90 (0.83-0.97) Anorexia 1.98 (0.83-4.75) 0.53 (0.26-1.10) 0.62 (0.12-1.11) 0.62 (0.12-1.12) Pharyngeal exudate 1.85 (1.58-2.16) 0.78 (0.74-0.82) 0.38 (0.32-0.44) 0.79 (0.73-0.84) Vomiting 1.79 (1.56-2.06) 0.85 (0.81-0.90) 0.28 (0.21-0.36) 0.84 (0.79-0.89) Tender cervical nodes 1.72 (1.54-1.93) 0.78 (0.75-0.81) 0.40 (0.35-0.46) 0.77 (0.71-0.82) Sibling with sore throat 1.71 (0.82-3.53) 0.92 (0.82-1.03) 0.18 (0.14-0.23) 0.89 (0.83-0.94) Halitosis 1.54 (0.79-2.99) 0.95 (0.81-1.12) 0.12 (0.05-0.29) 0.92 (0.86-0.99) Tonsillar and/or pharyngeal exudate 1.40 (1.10-1.77) 0.86 (0.75-0.98) 0.37 (0.28-0.46) 0.74 (0.68-0.78) Large cervical nodes 1.39 (1.16-1.67) 0.67 (0.53-0.84) 0.64 (0.50-0.76) 0.54 (0.41-0.67) Lack of cough 1.36 (1.18-1.56) 0.59 (0.48-0.73) 0.73 (0.66-0.78) 0.46 (0.38-0.55) Tonsillar exudates 1.35 (0.98-1.87) 0.81 (0.63-1.06) 0.46 (0.27-0.67) 0.66 (0.48-0.80) Tonsillar swelling 1.27 (1.04-1.54) 0.67 (0.52-0.85) 0.70 (0.64-0.76) 0.44 (0.32-0.57) Dysphagia 1.22 (1.00-1.48) 0.68 (0.51-0.91) 0.72 (0.55-0.85) 0.41 (0.23-0.62) Headache 1.22 (0.95-1.57) 0.90 (0.77-1.04) 0.39 (0.28-0.51) 0.68 (0.58-0.76) Lack of coryza 1.21 (1.08-1.35) 0.69 (0.55-0.88) 0.72 (0.64-0.79) 0.40 (0.34-0.48) Abdominal pain 1.18 (0.92-1.51) 0.95 (0.89-1.03) 0.24 (0.19-0.30) 0.79 (0.75-0.83) Red tonsils and/or pharynx 1.13 (0.96-1.33) 0.41 (0.16-1.02) 0.93 (0.85-0.96) 0.18 (0.09-0.35) Reported fever 1.07 (0.96-1.19) 0.86 (0.67-1.11) 0.71 (0.58-0.82) 0.33 (0.23-0.49) Red tonsils 1.07 (0.86-1.34) 0.82 (0.40-1.69) 0.80 (0.60-1.00) 0.25 (0.00-0.51) Red pharynx 1.06 (0.95-1.18) 0.56 (0.27-1.17) 0.93 (0.81-0.98) 0.12 (0.03-0.34) Documented temperature >38° or >38.5°C 1.02 (0.87-1.21) 0.98 (0.83-1.15) 0.50 (0.36-0.63) 0.51 (0.38-0.65) Summer 0.86 (0.61-1.20) 1.02 (1.00-1.05) 0.13 (0.00-0.33) 0.85 (0.65-1.04) Arthralgia 0.74 (0.18-3.08) 1.02 (0.97-1.06) 0.09 (0.00-0.25) 0.90 (0.77-1.04) Conjunctivitis 0.73 (0.46-1.16) 1.02 (0.98-1.05) 0.05 (0.02-0.11) 0.94 (0.85-0.98) Acute otitis media 0.65 (0.14-2.91) 1.04 (0.93-1.16) 0.03 (0.01-0.05) 0.94 (0.84-1.04) History of tonsillectomy 0.64 (0.49-0.84) 1.07 (1.03-1.11) 0.11 (0.08-0.13) 0.84 (0.81-0.86) Hoarseness 0.62 (0.46-0.83) 1.04 (1.03-1.06) 0.06 (0.03-0.12) 0.90 (0.85-0.93) Diarrhea 0.51 (0.33-0.79) 1.04 (0.99-1.11) 0.03 (0.00-0.06) 0.93 (0.86
Modified from: Shaikh et al. 2012
This post and podcast are dedicated to Sarah Werner for her constant encouragement of the story in all of us. Check out Write Now with Sarah Werner.
Selected References
Cheung L et al. Throat swab have no influence on the management of patients with sore throats. J Laryngol. 217; 131:977-981.
Ebell MH et al. Rational Clinical Examination: Does This Patient Have Streptococcal Pharyngitis? JAMA. 2000;284(22):2912-2918
Homme JH et al. Duration of Group A Streptococcus PCR positivity following antibiotic treatment of pharyngitis. Diagn Microbiol Infect Dis. 2018 Feb;90(2):105-108.
Nakhoul GN et al. Management of Adults with Acute Streptococcal Pharyngitis: Minimal Value for Backup Strep Testing and Overuse of Antibiotics. J Gen Intern Med. 2013 Jun; 28(6): 830–834.
Oliver J et al. Group A Streptococcus pharyngitis and pharyngeal carriage: A meta-analysis. PLoS Negl Trop Dis. 2018 Mar 19;12(3):e0006335.
Shaikh N, Leonard E, Martin JM. Prevalence of streptococcal pharyngitis and streptococcal carriage in children: a meta-analysis. Pediatrics. 2010 Sep;126(3):e557-64.
Shaikh et al. Accuracy and Precision of the Signs and Symptoms of Streptococcal Pharyngitis in Children: A Systematic Review. J Pediatrics. 2012; 3:487-493.e3
