Carbapenem-Resistant Klebsiella pneumoniae Now Infects Half of Clinical Cases in Iran, Landmark Analysis Finds

A sweeping synthesis of a decade of clinical microbiology data from Iran has delivered one of the starkest quantitative portraits yet of drug-resistant bacteria in the Middle East. Researchers at Tarbiat Modares University in Tehran pooled the results of 46 studies covering 6,708 clinical isolates of Klebsiella pneumoniae and found that just over half of these hospital-derived bacteria were resistant to carbapenems, the last-line antibiotics that physicians typically reserve for the most serious infections. The finding, published in BMC Infectious Diseases, transforms what has long been a patchwork of single-hospital reports into a coherent national picture, and the picture is alarming.

Klebsiella pneumoniae is not an exotic pathogen. It is a common inhabitant of the human gut and an opportunistic foe in hospitals, where it causes pneumonia, bloodstream infections, urinary tract infections, and wound infections, particularly among patients with weakened immune systems or indwelling medical devices. What makes the bacterium dangerous is its remarkable capacity to acquire and share resistance genes. When K. pneumoniae becomes resistant to carbapenems, a class of beta-lactam antibiotics structurally engineered to survive most defensive enzymes, clinicians are pushed toward older, more toxic drugs such as colistin and tigecycline, options that carry significant side effects and uncertain outcomes.

The new analysis, led by Leila Shamkhali, Raheleh Karimiravesh, and Neda Baseri, set out to answer two questions with statistical rigor: how common is carbapenem-resistant K. pneumoniae, or CRKP, among clinical isolates in Iran, and which resistance genes are driving the phenomenon. The team searched PubMed/MEDLINE, Scopus, ScienceDirect, Springer, Wiley Online Library, Google Scholar, and the Iranian Scientific Information Database for studies published between January 2015 and December 2025. Only studies involving clinical isolates from human patients, and only those reporting sufficient prevalence data on carbapenem resistance or carbapenemase genes, made the cut. Studies based exclusively on non-clinical samples, such as environmental or animal isolates, were excluded to keep the analysis anchored to genuine human disease.

The statistical machinery behind the paper followed the standard playbook for modern meta-analysis. Because individual studies differ in size, geography, and methodology, the researchers used a random-effects model, which assumes that the true prevalence may genuinely vary from one setting to another rather than assuming a single fixed value. Heterogeneity, the degree of variation among studies, was quantified with Cochran’s Q test and the I-squared statistic, while potential small-study effects, the tendency for smaller studies to report more extreme results, were probed with Egger’s regression test. All analyses were run in R software, version 4.5.2, and the authors note that AI-assisted tools were used for language editing and statistical support, with all outputs independently verified by the team.

The headline number is sobering. Across the 46 included studies, the pooled prevalence of carbapenem resistance among clinical K. pneumoniae isolates was 51 percent, with a 95 percent confidence interval stretching from 38 to 63.9 percent. In practical terms, roughly one in every two K. pneumoniae isolates recovered from Iranian patients in the included studies could shrug off carbapenem therapy. The confidence interval is wide, and that width matters: it reflects enormous heterogeneity among the studies, with an I-squared value of 96.1 percent and a P value below 0.001. Such extreme heterogeneity means the pooled figure should be read as a central tendency across very different hospitals, regions, and sampling strategies, not as a uniform national rate.

Why does heterogeneity run so high? The answer lies in the biology and the sociology of resistance. Carbapenem resistance is not evenly distributed; it clusters in intensive care units, in tertiary referral centers, and in regions where antibiotic use is less tightly controlled. A study conducted in a major Tehran teaching hospital’s ICU will inevitably report higher resistance than one drawing from community clinics. Methodological differences compound the problem: some studies define resistance phenotypically using disk diffusion or minimum inhibitory concentration testing, while others confirm it molecularly, and the thresholds and carbapenem drugs tested can vary. The random-effects model absorbs this variation statistically, but it cannot eliminate the underlying diversity of the evidence base.

Beneath the resistance phenotype lies a molecular arsenal, and the meta-analysis mapped it gene by gene. Carbapenemases are enzymes that hydrolyze the beta-lactam ring at the heart of carbapenem antibiotics, and they are encoded by genes that bacteria can carry on plasmids, mobile DNA elements that shuttle readily between strains and even between species. Among Iranian clinical isolates, the blaOXA-48-like family dominated, with a pooled prevalence of 66 percent, though with a very wide confidence interval of 25 to 92 percent. The closely related blaOXA-48 gene itself was detected in 45 percent of isolates, while blaNDM, a metallo-beta-lactamase gene of growing global concern, appeared in 29 percent. The genes blaKPC, blaVIM, and blaIMP trailed at 26, 18, and 12 percent respectively.

The dominance of OXA-48-like enzymes is epidemiologically significant. These enzymes, originally described in Turkey and now endemic across the Middle East, North Africa, and Europe, hydrolyze carbapenems efficiently but spare extended-spectrum cephalosporins, meaning bacteria carrying them can appear deceptively susceptible on routine screening unless specific carbapenem testing is performed. NDM carbapenemases, by contrast, belong to the metallo-beta-lactamase class and inactivate nearly all beta-lactams except aztreonam, and they are notoriously difficult to inhibit with available beta-lactamase inhibitor drugs. The co-circulation of both gene families in Iranian hospitals raises the specter of strains acquiring multiple carbapenemases simultaneously, a scenario that effectively exhausts the beta-lactam class entirely.

The authors are careful about the limitations inherent in their approach, and readers should be too. Egger’s regression test and funnel plot analyses, reported in the supplementary materials for each gene, were used to assess publication bias, the risk that studies finding high prevalence were more likely to be published than those finding low prevalence. Trim-and-fill sensitivity analyses were applied to the blaVIM and blaIMP estimates. Quality assessment using the Newcastle-Ottawa Scale evaluated the methodological soundness of the included studies. Even so, a meta-analysis can only be as representative as the studies it aggregates, and the concentration of research in certain provinces and hospital types may skew the national picture in ways no statistical adjustment can fully correct.

What emerges from this work is less a single statistic than a call to action. The authors conclude that CRKP represents a major public health concern in Iran and highlight an urgent need for continuous molecular surveillance, strengthened antimicrobial stewardship, and effective infection prevention and control measures. Molecular surveillance matters because phenotypic testing alone cannot distinguish an OXA-48 strain from an NDM strain, and that distinction shapes both treatment decisions and outbreak investigations. Stewardship programs, which restrain the indiscriminate use of broad-spectrum antibiotics, reduce the selective pressure that allows resistant strains to flourish. And infection control, from hand hygiene to contact precautions for colonized patients, remains the most direct brake on transmission. As carbapenem-resistant Enterobacterales continue their global march, the Iranian data serve as both a warning and a template: systematic, molecularly informed surveillance is the only way to see the enemy clearly, and the enemy, by this count, is already in half the wards.

Subject of Research: Prevalence of carbapenem-resistant Klebsiella pneumoniae and carbapenemase-encoding genes among clinical isolates in Iran

Article Title: Prevalence of carbapenem-resistant Klebsiella pneumoniae and associated carbapenemase genes among clinical isolates in Iran: a systematic review and meta-analysis

Article References: Shamkhali, L., Karimiravesh, R., & Baseri, N. (2026). Prevalence of carbapenem-resistant Klebsiella pneumoniae and associated carbapenemase genes among clinical isolates in Iran: a systematic review and meta-analysis. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14488-9

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14488-9

Keywords: Klebsiella pneumoniae, carbapenem resistance, carbapenemase genes, OXA-48, NDM, antimicrobial resistance, Iran, meta-analysis, hospital infections, infection control, antimicrobial stewardship, public health