PHILADELPHIA — Long-term antibiotic therapy for patients with acne induces complex immunologic and microbial changes that can have surprising clinical consequences not only for the patients but also for their close contacts, Whitney P. Bowe reported at the annual meeting of the Society for Investigative Dermatology.
For the last few years, researchers at the University of Pennsylvania, under the direction of Dr. David Margolis, have been exploring the microbial ecology of acne patients and the ways in which it is affected by antibiotic treatment.
They have discovered several phenomena. For one, acne patients on antibiotics are twice as likely to develop upper respiratory tract infections (URIs) than are those not treated. They are also three times more likely to carry group A streptococci in the oropharynx.
Some investigators have suggested that close contacts of antibiotic-treated acne patients may also be at increased risk for infectious conditions. Dr. Margolis' team recently completed a study that examined this conjecture. Ms. Bowe, a medical student and member of Dr. Margolis' research team, presented the findings in a poster.
The team analyzed data from the General Practice Research Database, which is an ongoing United Kingdom registry, and they determined rates of URIs among household contacts of acne patients.
They obtained data on 81,480 contacts of acne patients without URIs and 16,614 contacts of patients who did have URIs. The two cohorts were nearly equivalent in terms of their age (mean of 37 years) and sex (about 50% male).
Not surprisingly, the contacts of acne patients with URIs were more likely to have URIs themselves. Just over 6% of those in contact with a URI-affected acne patient also had a URI, compared with only 4% among the contacts of URI-free patients. Though the absolute numbers were small, the difference was statistically significant. The adjusted odds ratio for URI was 1.44 for close contacts of individuals with acne and URIs, meaning that close contacts of individuals with acne and URIs have a 44% increased risk of having a URI themselves.
The important question, said Ms. Bowe, is whether antibiotic therapy had any influence on this. “Some researchers have postulated that antibiotic exposure of any individual may affect the infectious illnesses of everyone in a group. One of our goals was to determine which factor plays more of a role in predicting URI in a household contact: exposure to an acne patient with a symptomatic URI or exposure to an acne patient on antibiotics.”
The answer proved clearly to be the former. The odds ratio for having a URI was 0.94 in household contacts of antibiotic-treated acne patients who did not have a URI and 0.71 in contacts of acne patients who had URIs and took antibiotics.
Contrary to some researchers' expectations, frequent exposure to an antibiotic-using acne patient seems to lower rather than raise the risk of URI among household contacts.
Whereas ongoing antibiotic therapy appears to increase the chances that an acne patient will develop a URI, the development of similar infections in household contacts is most likely owing to direct transmission of the pathogen and not to any increased susceptibility related to the patient's antibiotic use, as some have hypothesized.
“Although acne patients on antibiotics are about two times more likely to develop URIs, they appear to be less likely to transmit these URIs to their household contacts,” commented Ms. Bowe. “While this is reassuring from a public health perspective, the finding likely supports the hypothesis that acne antibiotics are immunomodulatory, predisposing acne patients to infections from pathogens that are not virulent enough to cause infection in fully immunocompetent hosts.”