What is the frequency of antimicrobial-resistance in Haemophilus influenzae infections?

Updated: Jun 11, 2021
  • Author: Joseph Adrian L Buensalido, MD; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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It is important to monitor the resistance rates of H influenzae to different antibiotics to guide empiric antimicrobial choices while awaiting susceptibility results. For instance, a study of 117 H influenzae isolates in Poland showed that susceptibilities to ampicillin and amoxicillin were below 80%, susceptibility to cefuroxime was just slightly above 80%, while susceptibilities to amoxicillin/clavulanate and ceftriaxone were close or equal to 100%, [57] making the latter two more reliable for empiric treatment in that locality.

Among 610 respiratory and vaginal isolates from pediatric patients in China, 51.5% were beta-lactamase–positive; 52.5% of isolates were resistance to ampicillin. The rates of susceptibility to ampicillin/sulbactam, cefotaxime, cefuroxime, clarithromycin, and sulfamethoxazole-trimethoprim were 95.9%, 96.4%, 72.1%, 81.8%, and 36.4%, respectively, [58] meaning that ampicillin/sulbactam and cefotaxime should be the primary choices for empiric treatment.

In a UK study, among 24 sputum specimens from patients with COPD that were positive for H influenzae, 67% were resistant to ampicillin (of which 56% were beta-lactamase–positive), 46% were resistant to erythromycin, and 0% were resistant to fluoroquinolones. [59]

In Canada from 2007-2014, NTHi comprised 54.6% of H influenzae isolates, and the 45.4% that were serotypeable were mostly Hia (23.1%), followed by Hib (8.3%), and then type f (10.8%). The resistance rate to ampicillin was 16.4%, and the percentage of beta-lactamase–producing isolates increased from 13.5% in 2007-2010 to 19% in 2011-2014. No resistance to third-generation cephalosporins and fluoroquinolones was observed, but resistance to trimethoprim/sulfamethoxazole was common. [60]

A study from Thailand’s largest national tertiary referral center collected 1126 H influenzae clinical isolates (sputum, adenoid tissue, bronchoalveolar lavage fluid) from patients ranging in age from 7 days to 96 years from October 2007 to June 2016. Almost all isolates were susceptible to amoxicillin/clavulanate, cefotaxime, ceftriaxone, cefuroxime, and ciprofloxacin, while the susceptibility rate to trimethoprim/sulfamethoxazole was only 50.1%, and more than 38% of isolates were resistant to ampicillin. [61]

In one Japanese study, most H influenzae isolates collected from patients with acute urethritis and/or epididymitis were susceptible to ceftriaxone, fluoroquinolones, macrolides, and tetracyclines, based on the recommended MIC breakpoints (Clinical and Laboratory Standards Institute). However, azithromycin treatment failures were noted in acute urethritis cases despite reports of azithromycin susceptibility. [62]

Another concerning finding from Japan is the prevalence of beta-lactamase–negative but ampicillin-resistant H influenzae isolates that are also macrolide resistant. [63]

The site of infection and the clinical response determine the length of antibiotic treatment.

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