Which bacteria cause blood infections in cancer patients, and resist drugs?
In one Iranian cancer hospital, most blood infections were caused by gram-negative bacteria, carbapenem resistance grew each year, and about one in five patients with these infections died.
Source
Bloodstream infections in adult patients with malignancy, epidemiology, microbiology, and risk factors associated with mortality and multi-drug resistance
Study at a glance
- Design
- Cohort — Retrospective review of blood-culture surveillance and hospital records at one oncology hospital in Shiraz, Iran, with logistic regression for mortality and multidrug-resistance predictors.
- N
- N=414 · 414 adult patients with a positive bacterial blood culture (fungal, contaminant and polymicrobial results excluded).
- Population
- Adults aged 18 or older with haematological malignancies or solid tumours admitted to a 100-bed oncology hospital who developed bacterial bloodstream infection.
- Outcome
- Causative organisms, antibiotic susceptibility and resistance (ESBL, carbapenem resistance, multidrug resistance), mortality, and predictors of multidrug-resistant gram-negative infection.
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What they did
The researchers reviewed records of 414 adults with cancer who had a bacterial bloodstream infection at a 100-bed oncology hospital in Shiraz, Iran, between July 2015 and August 2019. They recorded patient characteristics, the bacteria grown from blood cultures, and antibiotic susceptibility from disc-diffusion testing. They then used logistic regression to look for factors linked to death and to multidrug-resistant gram-negative infection.
What they found
Gram-negative bacteria caused 63.3% of infections, led by E. coli, Pseudomonas and Klebsiella pneumoniae, while coagulase-negative staphylococci were the commonest gram-positive cause. Among gram-negative infections, 39.3% were carbapenem-resistant and this rose significantly each year; nearly half met the definition of multidrug resistance. Mortality from gram-negative infections was about 20%, and no factor studied significantly predicted death. A low white-cell count and non-fermenting gram-negative bacteria (such as Pseudomonas) were linked to multidrug-resistant infection, and piperacillin-tazobactam, a standard first-line empiric drug there, performed poorly against resistant E. coli and Klebsiella.
The limits
What it doesn't show
Data came from one hospital, so resistance patterns may not apply elsewhere. Being retrospective, key details such as chemotherapy regimens and prior antibiotic use were often unavailable, leaving room for hidden bias in the risk-factor analyses. Carbapenemase enzyme types were not tested, and not every isolate was tested against every drug, so susceptibility percentages rest on varying denominators. The study describes associations and trends but cannot show that changing empiric therapy would reduce deaths.
Key terms
- Bloodstream infection (BSI)
- Bacteria growing in the blood with clinical signs such as fever, chills or low blood pressure, not explained by infection at another site.
- Febrile neutropenia
- Fever in a patient whose neutrophil count is very low, usually from chemotherapy; treated as an emergency with immediate empiric antibiotics.
- ESBL (extended-spectrum beta-lactamase)
- Bacterial enzymes that break down many penicillins and cephalosporins, making those antibiotics ineffective.
- Carbapenem-resistant gram-negative bacteria
- Gram-negative bacteria that resist carbapenems such as imipenem and meropenem, often last-line antibiotics.
- Multidrug resistance (MDR)
- Here, non-susceptibility to at least one agent in three or more antibiotic classes.
- Empiric antibiotic therapy
- Antibiotics started before culture results are known, chosen based on the most likely organisms and local resistance patterns.
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What type of study was this?
Common questions
Why does local resistance surveillance matter for cancer patients?
Patients with febrile neutropenia must start antibiotics before culture results return. If the usual empiric drug is ineffective against local resistant bacteria, patients may receive inadequate treatment, which raises mortality.
Did antibiotic resistance increase the risk of dying in this study?
Some resistant infections had higher death rates, but the differences were not statistically significant, and no factor studied significantly predicted mortality, possibly because of limited data and sample size.
Are these results true for all hospitals?
No. This is a single Iranian centre, and resistance rates vary widely between regions; the authors call for prospective multicentre studies.
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