Diagnostic Accuracy of the Simplified Carbapenem Inactivation Method versus the Modified Hodge Test in Carbapenem-Resistant Pseudomonas aeruginosa: A Cross-Sectional Study
Abstract
Background: Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is among the pathogens contributing most to the global burden of antimicrobial resistance, and its pooled prevalence in Indonesia reaches 43%. Carbapenem resistance and carbapenemase production are not equivalent, and only the enzymatic route is transmissible and therapeutically decisive. Molecular confirmation is unavailable in most Indonesian laboratories, so an accurate low-cost phenotypic assay is needed. Objective: To compare the simplified carbapenem inactivation method (sCIM) with the Modified Hodge Test (MHT) for detecting carbapenemase production in carbapenem-resistant P. aeruginosa. Methods: This cross-sectional diagnostic-accuracy study evaluated 30 meropenem- and imipenem-resistant clinical isolates archived at Dr. Soetomo General Academic Hospital, Surabaya, using PCR for blaIMP, blaGES, blaOXA, blaNDM, blaKPC and blaVIM as the reference standard. Result: A carbapenemase gene was detected in 13/30 isolates (43.3%): blaIMP in 9, blaGES in 3 and blaOXA in 1. sCIM achieved 92.31% sensitivity (95% confidence interval 64.0-99.8), 100.00% specificity (80.5-100.0), 96.7% accuracy and near-perfect agreement with PCR (kappa 0.932). MHT achieved 46.15% sensitivity (19.2-74.9), 88.24% specificity (63.6-98.5) and fair agreement (kappa 0.360). The paired exact McNemar test confirmed the sensitivity advantage of sCIM (p = 0.031), and bootstrapping showed a 26.6-percentage-point difference in overall accuracy (95% confidence interval 10.0-43.3). MHT detected no blaGES-positive isolate and only 6/9 blaIMP-positive isolates; sCIM detected all of both, while neither assay detected the single poorly expressed blaOXA isolate. Conclusion: sCIM is an accurate, rapid and inexpensive assay that should replace MHT in Indonesian laboratories and feed directly into stewardship and infection-control decisions.