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Levofloxacin-resistant H. influenzae increasing in Taiwan
Over a 6-year period, levofloxacin-resistant Haemophilus influenzae increased significantly in Taiwan, primarily driven by the spread of several clones in the elderly population in different regions, according to surveillance data.
“We studied a large number of levofloxacin-resistant H. influenzae from clinical diagnostic samples of multiple hospitals in different regions of Taiwan, so physicians should take into account the high rate of fluoroquinolone resistance when they prescribe empirical therapy for H. influenzae infections,” the authors wrote in their study published in Emerging Infectious Diseases. “Surveillance and intervention measures should be directed at the risk groups identified in this study to halt the increase in fluoroquinolone resistance in H. influenzae.”
Shu-Chen Kuo, MD, and colleagues analyzed data from the Taiwan Surveillance of Antimicrobial Resistance (TSAR), a biennial nationwide surveillance program.
From 2004-2010, 1,462 nonduplicate H. influenzae isolates were collected from 26 hospitals involved in the TSAR program. The resistance rate for levofloxacin rose from 2% in 2004 to 24.2% in 2010 (P<.001). Resistance to sparfloxacin (no longer available in the US) and trimethoprim/sulfamethoxazole also increased steadily and significantly during the study period.
The researchers found these levofloxacin-resistant isolates more often in elderly patients, from respiratory origins, from regional hospitals and inpatient settings and from central and southern Taiwan.
“We found age and regional differences in this resistance phenotype, which might have resulted from differences in fluoroquinolone use and patient populations,” the authors wrote.
While other surveillance data from around the world have found low fluoroquinolone resistance in H. influenza, fluoroquinolone resistance has been reported. A fluoroquinolone-resistant H. influenzae moved through a hospital-affiliated long-term care facility in New York in 2001; nearly all of the resistant isolates were related to a single clone. From 2002 to 2004, resistance rates increased from 0.5% to 2.6% in Hokkaido, Japan.
In this study, isolates of the same pulsed-field gel electrophoresis (PFGE) cluster had similar mutation patterns.
“Therefore, the emergence of fluoroquinolone-resistant isolates may be the result of several clones spreading in the same region,” the authors wrote.
The researchers did find isolates in the same PFGE cluster with the same sequence typing (ST) but different quinolone resistance-determining regions (QRDR) mutations.
“In addition, nearly all of the levofloxacin-resistant H. influenzae isolates belong to seven previously unreported STs or their single locus variants,” the authors wrote. “This finding indicates that the emergence of levofloxacin-resistant isolates likely occurred through spontaneous mutation of hypermutable clones under selective pressure, and these clones then disseminated locally in each region.”
Disclosure: The research was supported by intramural grants from the National Health Research Institutes.