Cats and dogs bring joy, comfort, and companionship to millions of people. But a new study published in Critical Care reminds us that, in rare cases, they can also carry bacteria that lead to severe infections—sometimes so serious that people end up in the intensive care unit (ICU) with life-threatening sepsis.

This large study, known as PETSEPSIS, looked back at the medical records of 174 adult patients admitted to 46 ICUs. All these patients had sepsis caused by bacteria commonly passed from pets to humans. The most frequent bacteria were Pasteurella, Bartonella, Capnocytophaga, and Francisella tularensis. These organisms are often found in the mouths or claws of cats and dogs and can be transmitted through bites, scratches, or even close contact with an animal’s saliva.

The results were striking. Nearly 25% of patients died during their hospital stay. More than half required life-support treatment such as mechanical ventilation or vasopressors to manage septic shock. A small number of patients, mostly those infected with Capnocytophaga, developed such severe illness that amputation of a limb was necessary.

One important takeaway from the study is that the type of bacteria involved did not predict who lived or died. Nor did the early choice of antibiotics seem to make a difference. Instead, the patients’ underlying health conditions played a much larger role in determining outcomes. People who were older, smoked, had liver or kidney disease, or were anaemic were much more likely to die from their infections. This highlights that host factors—not just the infection itself—are key in sepsis survival.

For clinicians, this study is a valuable reminder that pet exposure should not be overlooked in patients with sepsis, even if there is no clear history of a bite or scratch. Close contact with animals can still result in serious illness, especially in people with weakened immune systems or chronic conditions.

Although infections like these are rare, when they happen, they can progress very quickly and require aggressive care. The findings reinforce the importance of early recognition, careful attention to risk factors, and rapid escalation to ICU support in severe sepsis cases.

Reference

Quintin, J., Le Thuaut, A., Plouvier, F. et al. Characteristics and outcomes of ICU patients with sepsis transmitted by cats and dogs: the PETSEPSIS multicentre retrospective observational cohort study. Crit Care 29, 315 (2025). https://doi.org/10.1186/s13054-025-05558-6