A woman’s newly adopted cat may have brought her an unwelcome gift: a bacterial germ that caused her months of diarrhea. In a new case report this month, doctors say that the woman’s bout of recurrent Clostridioides difficile could have been fueled by her cat, who also tested positive for the bacteria. Thankfully, both the cat and the owner were eventually treated successfully, but the case might represent the first known instance of cat-to-human transmission of the infection.
Clostridioides difficile, also called C. diff, is a ubiquitous source of gastrointestinal misery, typically causing diarrhea and colitis (inflammation of the colon). It’s estimated that nearly half a million C. diff infections occur in the U.S. every year, according to the Centers for Disease Control and Prevention. But what makes the germ more pernicious is that it commonly reappears after the initial illness fades away, even with antibiotic treatment. About one in six people sickened by C. diff will become sick again within the following two to eight weeks, either from the original infection or catching a new one.
Recurrent C. diff is a painful experience for anyone, but it’s more common and outright life-threatening for already vulnerable people, such as the elderly and hospitalized. In 2017, there were an estimated 223,900 such cases in hospitalized patients and 12,800 related deaths in the United States.
One of the most important risk factors for C. diff is a preceding disruption of the gut microbiota, the community of normally harmless or beneficial bacteria that live along our digestive tract. This can happen after people take broad-spectrum antibiotics to treat other infections, which is one reason why C. diff is common in hospitals. However, the authors of this case report believe there was an added furry element to their patient’s infection.
According to their paper, published last week in the American Journal of Case Reports, the previously healthy 31-year-old patient first developed severe diarrhea soon after she finished a week’s course of antibiotics to treat a urinary tract infection. She was briefly monitored in the hospital, diagnosed with C. diff, and given a new two-week course of antibiotics.
The treatment seemed to work at first, but two months later, she returned to a primary care clinic with the same symptoms and once again tested positive for the infection. Continued antibiotic therapy was even less effective this time, and at a follow-up visit a month later she reported still having bouts of diarrhea, now about every four hours. During that visit, she asked if it was possible that her newly adopted cat—found as a stray a month before her illness began—could have contributed to her infection.
The woman was given different antibiotics, and she decided to have the cat examined by her vet and tested for C. diff. The cat did indeed test positive for the bacteria, though appeared to have no symptoms, and was given treatment. Right around that same time, the woman had been referred to a gastroenterologist, who prescribed her a new antibody-based treatment for her C. diff. The woman reported that her illness only began to clear up after both she and the cat were treated for their infection. And at a follow-up visit two months later, doctors confirmed that she was finally symptom-free.
“In conclusion, given the temporal relationship between the patient’s symptom onset and the adoption of the cat, and given the resolution of the patient’s symptoms following treatment of the cat, it is possible that the patient acquired C. difficile from the cat,” the authors wrote.
The authors’ hypothesis of the C. diff cat, it should be noted, is based on circumstantial evidence. There is other research suggesting that people can pass on the infection to their pets, but this would be the first known case of a pet transmitting C. diff to a human. It’s also possible that the transmission chain is even more complicated than it seems. The woman may have caught C. diff from somewhere else, which she then transmitted to her cat. At some point in between her multiple antibiotic treatments, the cat might have given it back to her, restarting the diarrhea carousel all over again. And of course, the cat could be entirely blameless here, their infection being a red herring that had nothing to do with their owner’s misery.
At the very least, the authors say, this case should provoke other doctors and researchers to further investigate whether pets and other animals that interact with people can be a reservoir for recurrent C. diff, which could be a more common public health threat even outside of hospitals.
“This case highlights the importance of comprehensive history taking and considers the zoonotic transmission of C. difficile as a novel” cause of community-acquired C. diff, the authors wrote.