Severity Assessment of Lower Respiratory Tract Infection in Malawi: Derivation of a Novel Index (SWAT-Bp) Which Outperforms CRB-65

OBJECTIVE: To assess the validity of CRB-65 (Confusion, Respiratory rate >30 breaths/min, BP<90/60 mmHg, age >65 years) as a pneumonia severity index in a Malawian hospital population, and determine whether an alternative score has greater accuracy in this setting. DESIGN: Forty three variables were prospectively recorded during the first 48 hours of admission in all patients admitted to Queen Elizabeth Central Hospital, Malawi, for management of lower respiratory tract infection over a two month period (N = 240). Calculation of sensitivity and specificity for CRB-65 in predicting mortality was followed by multivariate modeling to create a score with superior performance in this population. RESULTS: Median age 37, HIV prevalence 79.9%, overall mortality 18.3%. CRB-65 predicted mortality poorly, indicated by the area under the ROC curve of 0.649. Independent predictors of death were: Male sex, “S” (AOR 2.6); Wasting, “W” (AOR 6.6); non-ambulatory, “A” (AOR 2.5); Temp >38°C or <35°C, “T” (AOR 3.2); BP<100/60, “Bp” (AOR 3.7). Combining these factors to form a severity index (SWAT-Bp) predicted mortality with high sensitivity and specificity (AUC: 0.867). Mortality for scores 0–5 was 0%, 3.3%, 7.4%, 29.2%, 61.5% and 87.5% respectively. A score ≥3 was 84% sensitive and 77% specific for mortality prediction, with a negative predictive value of 95.8%. CONCLUSION: CRB-65 performs poorly in this population. The SWAT-Bp score can accurately stratify patients; ≤2 indicates non-severe infection (mortality 4.4%) and ≥3 severe illness (mortality 45%)

CRB-65 and SWAT-Bp scores; mortality prediction and test characteristics.

<p>CRB-65 and SWAT-Bp scores; mortality prediction and test characteristics.</p

ROC curves for mortality prediction by SWAT-Bp and CRB-65 scores.

<p>ROC curves for mortality prediction by SWAT-Bp and CRB-65 scores.</p

Validating a novel index (SWAT-Bp) to predict mortality risk of community-acquired pneumonia in Malawi.

Background Community-acquired pneumonia is a major cause of mortality worldwide. Early assessment and initiation of management improves outcomes. In higher-income countries, scores assist in predicting mortality from pneumonia. These have not been validated for use in most lower-income countries. Aim To validate a new score, the SWAT-Bp score, in predicting mortality risk of clinical community-acquired pneumonia amongst hospital admissions at Queen Elizabeth Central Hospital, Blantyre, Malawi. Methods The five variables constituting the SWAT-Bp score (male [S]ex, muscle [W]asting, non-[A]mbulatory, [T]emperature (>38°C or <35°C) and [B]lood [p]ressure (systolic<100 and/or diastolic<60)) were recorded for all patients with clinical presentation of a lower respiratory tract infection, presumed to be pneumonia, over four months (N=216). The sensitivity and specificity of the score were calculated to determine accuracy of predicting mortality risk. Results Median age was 35 years, HIV prevalence was 84.2% amongst known statuses, and mortality rate was 12.5%. Mortality for scores 0-5 was 0%, 8.5%, 12.7%, 19.0%, 28.6%, 100% respectively. Patients were stratified into three mortality risk groups dependent on their score. SWAT-Bp had moderate discriminatory power overall (AUROC 0.744). A SWAT-Bp score of ≥2 was 82% sensitive and 51% specific for predicting mortality, thereby assisting in identifying individuals with a lower mortality risk. Conclusion In this validation cohort, the SWAT-Bp score has not performed as well as in the derivation cohort. However, it could potentially assist clinicians identifying low-risk patients, enabling rapid prioritisation of treatment in a low-resource setting, as it helps contribute towards individual patient risk stratification