S. aureus Bacterium in Nose Not Linked with AAV Relapses, Study Suggests

The presence of the bacterium Staphylococcus aureus was not associated with a higher relapse rate of ANCA-associated vasculitis (AAV), a recent study suggests.

These results challenge the idea that use of certain antibiotics may prevent AAV relapses, the researchers said.

Titled “No evident association of nasal carriage of Staphylococcus aureus or its small-colony variants with cotrimoxazole use or ANCA-associated vasculitis relapses,” the study was published in Rheumatology.

Staphylococcus aureus (SA) is a type of bacteria that naturally lives in several areas of the human body, including in the nose and armpit, without causing problems. Under certain conditions, however, SA can become pathogenic, or disease-causing. It is the most common cause of staph infections.

AAV is an autoimmune disease in which the body produces antibodies that attack its own tissues  and cells. Some research has suggested that infections could play a role in this process. Essentially, the immune system could initially react to infectious agents like bacteria, leading to the production of autoantibodies that would harm the body.

Following this idea, it has also been suggested that bacteria — including SA — might increase the risk of exacerbations or relapses in AAV. This would, in turn, suggest that antibiotics could reduce the risk of relapses.

Indeed, some previous studies have shown that administering co-trimoxazole (CTX) — an antibiotic that is effective against SA and other bacteria — reduces the relapse rate in people with AAV. This has been postulated to be because the antibiotic kills SA. However, this treatment’s benefit remains controversial.

In the new study, researchers wondered whether the presence of SA in the nasal cavities of people with AAV — where the bacteria can exist harmlessly, but may also serve as a source for infections — would be predictive of a higher relapse rate.

To test this, the investigators took nasal samples from 119 people with AAV, as well as 88 people without the disease (controls). These samples were tested for the presence of SA, as well as the occurrence of a particular type of SA called the small-colony variant (SCV), which is involved in persistent infections of the airway. The researchers looked for patterns in the participants’ clinical data based on the presence of SA and/or SCV.

The rates of SA were not significantly different between the groups with and without AAV, although SCV was present at higher rates among people with ANCA vasculitis (11.9% vs. 1.1%).

Among people with AAV, rates of SA — but not SCV — were generally lower among those who were treated with CTX, although this difference was only statistically significant at certain doses, the researchers found. Interestingly, however, the presence of bacteria was not associated with AAV relapse rates.

“Nasal SA or SCV carriage was not associated with the frequency or severity of AAV,” the researchers said. “Moreover, we found no association between SA or SCV carriage and BVAS-assessed AAV activity, rhinitis, ANCA-positivity, CRP level [inflammation level], or AAV relapse(s).”

Rhinitis involves chronic sneezing or a congested, drippy nose with no apparent cause.

These results call into question the idea that CTX reduces the AAV relapse rate by killing bacteria. Although the antibiotic did seem to reduce the presence of the bacterium, this change “did not affect AAV evolution,” the researchers said.

Instead, they suggested that “the supposed CTX efficacy could be linked more to an anti-inflammatory than antimicrobial effect.”

The researchers said further study will be needed to validate this idea.