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Substantial macrolide resistance seen in M. genitalium in Denmark
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Nearly 40% of specimens positive for Mycoplasma genitalium were resistant to macrolides, according to researchers from Statens Serum Institut in Copenhagen, Denmark.
“[This finding emphasizes] the need for detection of resistance mutations to guide therapy,” they wrote in Clinical Infectious Diseases. “We suggest that testing guidelines for sexually transmitted infections are modified to include routine testing for M. genitalium and detection of macrolide resistance mediating mutations to ensure that treatment of genital tract infections is guided by etiologic diagnosis.”
The researchers conducted a retrospective survey of specimens received from 2006 to 2010. There were 31,600 specimens from 28,958 patients tested for M. genitalium during this time frame. The number of specimens tested increased per year, from 3,858 in 2006 to 7,361 in 2010. Most specimens (70%) were from women.
There were 1,414 specimens (4.9%) positive for M. genitalium. The proportion of patients positive for M. genitalium was higher among men: 9% vs. 3.1% for women. Within the study time frame, there was an increase in M. genitalium for both sexes. Among men, the rate increased from 7.9% to 10.3%, and for women, the rate increased from 2.4% to 3.8%.
Macrolide resistance testing was attempted for 1,121 positive specimens tested after Dec. 1, 2007, when macrolide resistance screening was introduced. Among the 1,085 specimens that completed resistance testing, 385 (38.2%) were resistant to macrolides. The most common mutations were A2058G, which accounted for 61% of the resistant specimens, and A2059G, accounting for 35%. There was a lower rate of macrolide resistance among patients tested at private specialists. The highest rate was among patients tested at STD clinics in hospitals.
“Although not documented in this report, we speculate that patients attending STD clinics may have a more risky sexual behavior than the general population and consequently have a higher risk of having had a previous [non-gonococcal urethritis] treated with the widely used single 1 g dose of azithromycin,” the researchers wrote. “This may have induced selection of azithromycin-resistant M. genitalium strains not detected initially.”
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Khalil Ghanem, MD, PhD
I think there are several points about this study that are worth highlighting. First, this is not a representative sample of the Danish population. Specimens were obtained mainly from symptomatic men and women, as well as asymptomatic women. Among those who had symptoms, testing for M. genitalium either occurred simultaneously with gonorrhea and chlamydia testing or after GC and CT testing. This can significantly impact prevalence estimates. I’d be very careful when trying to interpret trends. Second, this study does not provide data on symptoms, presence of co-infections, etc. Lastly, about 40% of the positive specimens had mutations associated with macrolide resistance. Again, we had limited data on how those who were treated with macrolides fared and how many were treated or retreated with a fluoroquinolone. Given the limitations of this study, I would be very careful in jumping to the conclusion that routine M. genitalium testing be performed on all patients with symptoms.
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