Background To evaluate therapy outcome in M genitalium infection with standard chlamydia treatment doxycyclin 9 days and azithromycin 1 g stat compared to extended azithromycin 15 g for 5 days and to evaluate macrolide resistance.

Methods Patients attending the STD-clinic in Falun, Sweden between January 1998 and December 2005 with a positive PCR test for M genitalium routinely had a test of cure. Response was determined to doxycycline, azithromycin 1 g as a single dose and 15 g extended treatment primary and secondary when persistence after doxycycline. Macrolide resistance was monitored at base as well as after treatment in those testing positive after treatment with azithromycin. Macrolide resistance also was monitored yearly 2006–2010 in patients with newly detected M genitalium infection.

Results Totally 313/407 (77%) had a test of cure, 254/313 (81%) within 12 weeks. The eradication rate with doxycycline was 43% totally, 46% for women and 38% for men, with azithromycin 1 g 92% totally, 96% for women and 89% for men and with azithromycin extended dosage 96% totally, 100% for women and 93% for men. Confirmed macrolide resistance developed in 7/7 (100%) of those testing positive after azithromycin 1 g. In 2006–2007 we found no, in 2008 and 2009 1/year and in 2010 11 patients with macrolide resistance in newly detected M genitalium.

Conclusions These findings confirms the results from other studies that doxycycline is inefficient in eradicating infection with M genitalium. Although the treatment outcome with azithromycin 1 g was not significantly lower than with extended dosage for 5 days it was in this study associated with 100% induced macrolide resistance in those with treatment failure. A remarkable higher proportion of macrolide resistance in 2010 than earlier years was found. We will try to monitor yearly prescription of azithromycin 1 g in our county and all Sweden last years. Is there an increase explaining the higher proportion 2010? Azithromycine 1 g should be avoided as recommended therapy for M genitalium as well as for chlamydia and non-gonococcal urethritis. Specific diagnostics for M genitalium as well as monitoring of resistance is urgent.