Research shows that healthy dogs and cats can transmit dangerous microbes to humans – and vice versa

Healthy dogs and cats can transmit multidrug-resistant organisms (MDROs) to their hospitalized owners, while humans can also pass these microbes on to their pets, according to research to be presented at the European Congress of Clinical Microbiology & Infectious Diseases. The study highlights the potential transmission of antibiotic-resistant bacteria between pets and humans.

Multidrug-resistant organisms can be passed between healthy dogs and cats and their hospitalized owners.

Fortunately, only a small number of cases have been found suggesting that pets are not a major source of antibiotic-resistant infections in hospitalized patients.

Healthy dogs and cats can pass on multidrug-resistant organisms (MDROs; bacteria that resist treatment with more than one antibiotic) to their hospitalized owners, and similarly, humans can pass these dangerous microbes on to their pets, according to new research being presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) this year in Copenhagen, Denmark (April 15-18).

The study of more than 2,800 hospital patients and their companion animals was conducted by Dr. Carolin Hackmann of Charité University Hospital Berlin, Germany, and colleagues.

“Our findings confirm that sharing of multidrug-resistant organisms between companion animals and their owners is possible,” said Dr. Hackmann. “However, we have only identified a handful of cases suggesting that neither cat nor dog ownership is a major risk factor for multidrug-resistant organism colonization in hospitalized patients.”

The role of pets as potential reservoirs of MDROs is of growing concern worldwide. Antimicrobial resistance occurs when infection-causing microbes (such as bacteria, viruses, or fungi) evolve to become resistant to the drug designed to kill them. Estimates suggest that antimicrobial-resistant infections caused nearly 1.3 million deaths in 2019 and were associated with nearly 5 million deaths worldwide.[1]

In this case-control study, researchers wanted to find out whether pets (ie cats and dogs) play a role in the infection of hospital patients with MDROs.

They focused on the most common superbugs in hospital patients: methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), 3rd generation cephalosporin-resistant Enterobacterales (3GCRE), and carbapenem-resistant Enterobacterales (CRE), which are resistant to multiple antibiotics including penicillin and cephalosporins.

Between June 2019 and September 2022, nasal and rectal swabs were collected from 2,891 patients admitted to Charité University Hospital Berlin (1,184 patients with previous colonization or colonization on admission and 1,707 newly admitted patients as controls), and from all dogs and cats in their households.

Genetic sequencing was used to identify both[{” attribute=””>species of bacteria in each sample, and the presence of drug-resistance genes. Whole genome sequencing was used to confirm the possible sharing of resistant bacteria.

Participants were also asked about well-known risk factors for MDROs (e.g., recent MDRO infections or use of antibiotics, recent hospital stays, presence of urinary or central venous catheters), as well as information about the number of pets in the household, the closeness of contact, and pet health.

Overall, 30% (871/2,891) of hospital patients tested positive for MDROs, and 70% (2,020/2,891) tested negative. The rate of dog ownership was 11% (93/871) and cat ownership 9% (80/871) in those who tested MDRO-positive, and 13% (267/2,020 and 253/2,020 respectively) in MDRO-negatives.

All 626 pet owners were asked to send throat and stool swab samples of their pets. Overall, 300 pet owners sent back samples from 400 pets. Of these samples, 15% (30/203) of dogs and 5% (9/197) of cats tested positive for at least one MDRO. In four cases, MDROs were phenotypically matching (MDROs were the same species and showed the same antibiotic resistance) between pets and their owners.

Whole genome sequencing confirmed that only one of the matching pairs was genetically identical in a dog and its owner. The matching pathogen was 3GCR Escherichia coli (common in the intestines of healthy people and animals).

“Although the level of sharing between hospital patients and their pets in our study is very low, carriers can shed bacteria into their environment for months, and they can be a source of infection for other more vulnerable people in the hospital such as those with a weak immune system and the very young or old,” says Dr. Hackmann.

This is an observational study and cannot prove that close contact with pets causes colonization with MDROs, but only suggest the possibility of co-carriage, while the direction of transfer is unclear. The authors point to several limitations, including a possible under-reporting of MDRO colonization in pets due to problems in taking swab samples, which was done by the pet owners themselves. Finally, the study results apply to the setting of hospital patients in an urban area and therefore may not be applicable to the general population or MDRO high-risk groups like livestock farmers.


  1. “Global burden of bacterial antimicrobial resistance in 2019: a systematic analysis” by Antimicrobial Resistance Collaborators, 19 January 2022, The Lancet.
    DOI: 10.1016/S0140-6736(21)02724-0

Meeting: European Society of Clinical Microbiology and Infectious Diseases (ECCMID) 2023

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