Because they are prone to rehospitalization, typically demand intensive hands-on care and are heavy users of antibiotics, advanced dementia residents in nursing homes commonly harbor dangerous strains of drug-resistant bacteria, according to new research published this week.

And as incubators of more than their share of such bacteria, they are among the most vulnerable nursing home residents to serious infections, researchers conclude in the latest issue of Infection Control & Hospital Epidemiology.

The study found that 1 in 5 nursing home residents with advanced dementia harbor strains of drug-resistant bacteria and more than 10% of the drug-resistant bacteria are resistant to four or more antibiotic classes, including ciprofloxacin, gentamicin and extended-spectrum penicillins. This creates the potential for once-treatable disease to spread easily in hospital-like settings, according to Erika D’Agata, M.D., an infectious disease physician at Rhode Island Hospital and lead author of the study.

The yearlong research involved 152 nursing home residents with advanced dementia in 22 facilities in the greater Boston area. Genetically related bacteria were detected in 18 of the 22 nursing homes (82%), according to the study. Drug-resistant Escherichia coli (E.coli) and Proteus mirabilis (P.mirabilis) were the most common bacteria discovered in study subjects.