CASH-75 – Atypical Pneumonia Predictor Score

Written by Rebecca Breed

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Using the CASH-75 score helped predict the absence of atypical pathogens (L. pneumophila or M. pneumoniae) as the causative agents of community acquired pneumonia (CAP) in hospitalized patients.

Why does this matter?
Antimicrobial stewardship improves antibiotic resistance, cost of care, and medication side effects. Fewer antibiotics, narrower spectrum, and shorter duration are good goals. However, the study we covered last week showed lower mortality among patients with CAP and culture-confirmed bacteremic pneumococcal pneumonia who received a macrolide, suggesting broader coverage might be better. If we could reliably predict that a patient’s pneumonia is not caused by an atypical agent, could we omit atypical coverage – such as a macrolide, fluoroquinolone, or doxycycline – and use a beta-lactam (such as a penicillin or cephalosporin)?

This study was a secondary analysis of a Swiss multicenter randomized controlled trial in adult patients hospitalized for CAP. A total of 580 patients were included, and atypical pathogens were causative in 31 patients (16 L. pneumophila and 15 M. pneumoniae) for a prevalence of 5.34%. These atypical pathogens were considered causative if detected by blood culture, PCR, or urinary antigen (for L. pneumophila) AND there was no other detected bacterial pathogen. The five clinical features can be remembered by the name of the score (“CASH-75”): absence of Chest pain, illness in Autumn, Sodium < 135 mmol/L, Heart failure and age < 75 years. These factors were all weighted equally. The higher the score, the greater the probability of atypical pneumonia. If the composite score was < 2, sensitivity is 100% and NPV 100% for absence of atypical pathogen. If increased to <3, sensitivity was 70%, but NPV remained high at 98%. The composite score had an AUC of 0.78 (95% CI = 0.71-0.85), which authors noted was similar to other scores used to predict the etiology of pneumonia. As mentioned, the authors provided two different cut-offs for the score, with differing sensitivities and NPVs. They noted that the cutoff of < 3 had the highest diagnostic odds-ratio, but this also allowed for some flexibility in terms of provider comfort in choosing what cutoff to use. Overall, there were a low number of total patients with atypical pneumonia, and the study needs external validation; however, it shows promise in helping providers determine when to add additional antibiotic coverage when admitting patients with CAP from the ED.

Editor’s note: After last week’s study showing lower mortality among patients with CAP who received a macrolide and had confirmed bacteremic pneumococcal pneumonia (which is not atypical), I am not sure how to think about this. I think this study is promising as well, but I will likely continue to follow IDSA guidelines and add atypical coverage for hospitalized patients with CAP until further evidence clarifies this question. ~Clay Smith

Accuracy of a score predicting the presence of an atypical pathogen in hospitalized patients with moderately severe community-acquired pneumonia. BMC Infect Dis. 2022 May 3;22(1):424. doi: 10.1186/s12879-022-07423-1.

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