Superbug Strains Carrying Two Carbapenemase Genes Triple Death Risk in ICU Patients

One of the most feared drug-resistant bacteria in the world has just become more dangerous still. A prospective study from a tertiary care hospital in South India has found that patients infected with carbapenem-resistant Klebsiella pneumoniae that carries two carbapenemase genes at once face markedly higher odds of dying within 28 days than those infected with strains carrying only a single resistance enzyme. The research, published in BMC Infectious Diseases, followed 106 intensive care unit patients with culture-confirmed infections and offers some of the clearest clinical evidence yet that dual carbapenemase co-production is not merely a laboratory curiosity but a genuine predictor of survival.

Klebsiella pneumoniae is a common inhabitant of the human gut and an opportunistic pathogen that can cause pneumonia, bloodstream infections, urinary tract infections, and wound infections, particularly in hospitalized and immunocompromised patients. When the bacterium acquires carbapenemases, enzymes that hydrolyze carbapenems, a class of last-resort beta-lactam antibiotics, treatment options collapse to a handful of toxic or expensive drugs. The World Health Organization classifies carbapenem-resistant K. pneumoniae as a critical priority pathogen, and the burden falls disproportionately on South Asia, where resistance genes circulate widely in hospitals and communities alike.

The enzymes involved are mechanistically distinct. The bla_NDM gene encodes New Delhi metallo-beta-lactamase, a metallo-enzyme that destroys nearly all beta-lactam antibiotics including carbapenems. The bla_OXA-48-like family encodes oxacillinases that are less potent against broad-spectrum cephalosporins but are highly efficient carbapenem hydrolyzers and are notoriously difficult to detect in routine phenotypic testing. When a single isolate carries both genes, the bacterium effectively deploys two independent biochemical strategies against the same class of drugs, and laboratory susceptibility testing can understate the true resistance arsenal. The new study set out to determine whether this molecular redundancy translates into worse outcomes at the bedside.

Researchers led by Pravalika Sathyanarayana, Sharadadevi Y Mannur, and Mahadevamma Lingaiah conducted a prospective observational study at a tertiary care hospital in South India between January 2024 and January 2025. They enrolled ICU patients with culture-confirmed carbapenem-resistant K. pneumoniae infections and used real-time polymerase chain reaction to detect five carbapenemase genes: bla_NDM, bla_OXA-48-like, bla_IMP, bla_VIM, and bla_KPC. Patients were stratified into four genotypic groups, those carrying bla_NDM alone, those carrying bla_OXA-48-like alone, co-producers carrying both, and non-producers, and the primary outcome was 28-day all-cause in-hospital mortality. Written informed consent was obtained from patients or their legally authorized representatives, and the study was approved by the institutional ethics committee and conducted under the Declaration of Helsinki.

The molecular findings were striking. Of the 106 patients, 30, or 28.3 percent, harbored isolates that co-produced both carbapenemases, while 16 patients, or 15.1 percent, died within 28 days of infection. Mortality varied significantly across genotypes, and the highest proportion of deaths occurred among patients infected with co-producing isolates, with 9 of 30 such patients, or 30 percent, dying within the follow-up window. That is roughly double the overall cohort mortality rate and suggests that the dual-enzyme phenotype marks a subset of infections that behave differently in critically ill hosts.

To quantify these associations, the team used Firth penalized logistic regression, a statistical approach designed for situations where outcome events are sparse and conventional maximum-likelihood models can fail or produce unstable estimates. In univariable analysis, mechanical ventilation was associated with a 12.47-fold increase in the odds of 28-day mortality, septic shock with a 25.11-fold increase, and each point increase on the APACHE II illness-severity score with a 29 percent increase in odds. Co-producer status itself carried an unadjusted odds ratio of 4.09, meaning patients with dual-carbapenemase isolates had roughly four times the odds of death compared with the rest of the cohort, a statistically significant association.

The exploratory multivariable model, which adjusted for these competing risk factors, retained three independent predictors: higher APACHE II score with an adjusted odds ratio of 1.24, septic shock with an adjusted odds ratio of 12.23, and carbapenemase co-production with an adjusted odds ratio of 7.50. In other words, even after accounting for how sick patients were on admission and whether they had progressed to septic shock, carrying a dual-carbapenemase strain was associated with more than a sevenfold increase in the odds of dying within 28 days. Model diagnostics showed no problematic multicollinearity, with variance inflation factors ranging from 1.12 to 1.28, and the apparent area under the receiver operating characteristic curve reached 0.975, indicating strong discrimination within this dataset.

The authors are careful to frame these numbers with appropriate scientific caution. The adjusted odds ratio for co-production of 7.50 came with a 95 percent confidence interval stretching from 1.50 to 51.67, an extraordinarily wide range that reflects the limited number of mortality events in the cohort. With only 16 deaths distributed across four genotypic groups, the point estimate is statistically significant but the true magnitude of the effect could plausibly be anywhere from a modest doubling of risk to a fifty-fold increase. The adjusted analysis was therefore explicitly labeled exploratory, and the apparent AUC of 0.975 was not internally validated, meaning its impressive value may partly reflect overfitting to this particular sample.

Residual confounding also looms over the findings. The study did not capture detailed data on antimicrobial management or source control, the surgical or procedural measures used to eliminate the focus of infection, and both are powerful determinants of survival in severe bacterial sepsis. It is conceivable that patients with co-producing strains received less effective empiric therapy, or that their infections were harder to eradicate for reasons unrelated to the resistance genes themselves. The single-center design further limits generalizability, since gene prevalence, prescribing patterns, and ICU case mix vary widely across institutions and regions. The authors call for larger multicenter studies incorporating detailed treatment and source-control data to determine whether the association is reproducible.

Even with those caveats, the study carries a pointed message for clinicians and laboratories. Rapid molecular detection of carbapenemase genes, rather than reliance on phenotypic susceptibility panels alone, can identify high-risk co-producing strains early enough to inform therapy, infection control measures, and conversations with families about prognosis. It also reinforces the urgency of stewardship programs designed to slow the horizontal spread of these plasmid-borne genes, because every co-producing isolate that circulates in an ICU represents a patient population at elevated risk. As antimicrobial resistance continues to outpace the development of new antibiotics, studies like this one demonstrate that the genetic composition of a pathogen is not just an epidemiological detail but a clinical variable that can mean the difference between recovery and death.

Subject of Research: Clinical impact of dual carbapenemase co-production on 28-day mortality in ICU patients with carbapenem-resistant Klebsiella pneumoniae: a prospective study from South India

Article Title: Clinical impact of dual carbapenemase co-production on 28-day mortality in ICU patients with carbapenem-resistant Klebsiella pneumoniae: a prospective study from South India

Article References: Sathyanarayana, P., Mannur, S. Y., & Lingaiah, M. (2026). Clinical impact of dual carbapenemase co-production on 28-day mortality in ICU patients with carbapenem-resistant Klebsiella pneumoniae: a prospective study from South India. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14539-1

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14539-1

Keywords: Clinical, impact, dual, carbapenemase, co-production, mortality, patients, carbapenem-resistant, Klebsiella, pneumoniae, prospective, South