31 July 2014
Four treatment failures of pharyngeal gonorrhoea with ceftriaxone (500 mg) or cefotaxime (500 mg), Sweden, 2013 and 2014
We describe four cases in Sweden of verified treatment failures of pharyngeal gonorrhoea with ceftriaxone (500 mg; n=3) or cefotaxime (500 mg; n=1) monotherapy. All the ceftriaxone treatment failures were caused by the internationally spreading multidrug-resistant gonococcal NG-MAST genogroup 1407 clone. Increased awareness of treatment failures is crucial particularly when antimicrobial monotherapy is used. Frequent test of cure and appropriate verification/falsification of suspected treatment failures, as well as implementation of recommended dual antimicrobial therapy are imperative.
This report describes four failures to treat pharyngeal gonorrhoea with ceftriaxone (500 mg; n=3) or cefotaxime (500 mg; n=1) in Sweden in 2013 and 2014.
Neisseria gonorrhoeae has developed resistance to all antimicrobials previously used as first-line treatment for gonorrhoea [1-4]. Clinical resistance is now emerging to the extended-spectrum cephalosporins (ESCs), i.e. cefixime (oral) and the more potent ceftriaxone (injectable). Many treatment failures with cefixime have been verified in Japan, Europe, Canada and South Africa. No failure to treat urogenital gonorrhoea with ceftriaxone (250 mg–1 g), the last remaining option for first-line empiric antimicrobial monotherapy, has been detected as yet. However, some few failures to treat pharyngeal gonorrhoea with ceftriaxone have been verified in Japan (n=1), Australia (n=3), Sweden (n=1) and Slovenia (n=1) [4-10]. In recent years, extensively drug-resistant (XDR) gonococcal strains with high-level ceftriaxone resistance were also reported from Japan, France and Spain [2,9-11].
From February to May 2013, three cases of suspected failure to treat pharyngeal gonorrhoea with ceftriaxone 500 mg intramuscularly were reported from two clinics for sexually transmitted infections (STIs) in Sweden (Table). All three patients reported having had unprotected oral and vaginal sex with heterosexual contacts in Stockholm. Case A was a woman in her 30s, with pharyngeal symptoms including pharyngitis. Cases B and C, both in their 50s, were asymptomatic. Pharyngeal and urogenital samples were taken and all patients had a positive gonococcal pharyngeal culture. Furthermore, the urogenital samples from the Cases B and C were positive in a nucleic acid amplification test (NAAT) (BD ProbeTec GC Qx Amplified DNA Assay, Becton Dickinson). All three patients were administered a single dose of 500 mg ceftriaxone intramuscularly (Day 1). When returning for follow-up after seven to 22 days, all patients were asymptomatic but had persistent positive gonococcal pharyngeal cultures. All urogenital samples were negative. Finally, all three patients were successfully treated with a single dose of 1 g ceftriaxone intramuscularly between Day 7 and 27, which was confirmed at follow-up visits with negative pharyngeal cultures between Day 22 and 48 (Table).
In May 2014, one case of suspected failure to treat pharyngeal gonorrhoea with cefotaxime 500 mg intramuscularly was reported from an STI clinic in Karlskrona, Sweden. This patient (Case D), a man in his 30s, attended the clinic because he had had unprotected oral and vaginal sex with a woman diagnosed with gonorrhoea. On Day 1, the patient was asymptomatic and sampled from the pharynx, urethra, and rectum. The pharyngeal sample was positive for gonococci in culture and he was treated with a single dose of 500 mg cefotaxime intramuscularly. At the follow-up visit (Day 7), the patient was still asymptomatic, however, a pharyngeal sample remained positive in culture. The patient was treated with a single dose of 250 mg ceftriaxone intramuscularly plus a single oral dose of 1 g azithromycin (day 14). On Day 26, the patient returned for test of cure and the pharyngeal culture was negative for gonococci (Table).
Table. Details of three verified ceftriaxone and one verified cefotaxime treatment failure of Neisseria gonorrhoeae pharyngeal infection, Sweden, 2013–2014*
Characterisation of N. gonorrhoeae isolates
The pre- and post-treatment gonococcal isolates were species-confirmed by sugar utilisation test, Phadebact Monoclonal GC Test (Pharmacia Diagnostics) and MaldiTOF MS (Bruker Daltonics). The paired isolates from each case were indistinguishable using N. gonorrhoeae multi-antigen sequence typing (NG-MAST ) and the isolates from Cases A, B and C belonged to the NG-MAST genogroup 1407 clone [4,13] (Table). Using Etest (AB bioMérieux), the isolates from Cases A, B and C (ceftriaxone treatment failures) showed elevated minimum inhibitory concentrations (MICs), i.e. 0.064–0.125 mg/L, which is equal to the European resistance breakpoint (>0.125 mg/L) . In Case D (cefotaxime treatment failure), according to the European resistance breakpoints , the paired isolates were resistant to cefotaxime (MIC: 0.5 mg/L) and the pre-treatment isolate also to ceftriaxone (MIC: 0.25 mg/L) (Table).
Sequencing of ESC resistance determinants [1,3,4,6,9,10,15] showed that all the paired isolates belonging to Cases A, B and C contained the penA mosaic allele XXXIV, which has been correlated with NG-MAST genogroup 1407, decreased susceptibility or resistance to ESCs and ESC treatment failures [1,4-6,9,11]. The isolates from Case D contained the penA mosaic allele XIII . In addition, all isolates contained mtrR and penB alterations that further increase the ESC MICs [1,3-6,9-11,15].
This paper reports four cases of verified pharyngeal gonorrhoea treatment failure in Sweden using injectable ESCs, i.e. ceftriaxone (n=3) and cefotaxime (n=1). The failures were verified in accordance with international recommendations [2,4], i.e. clinical records were obtained, reinfection was excluded, pre- and post-treatment isolates were identical using highly discriminatory molecular epidemiological typing, and the isolates had elevated ESC MICs and well recognised ESC resistance determinants. Reinfection was considered to be excluded as much as possible for all cases. Accordingly, all patients were strongly advised to abstain from any sexual contacts before their follow-up visit and all four patients repeatedly assured that they had not had any unprotected sexual contacts between the ceftriaxone/cefotaxime treatment and test of cure. Furthermore, Case D was infected by a casual sexual contact.
In the current emergent situation of fear that gonorrhoea may become untreatable [1-3,10], recommendations of using dual antimicrobial therapy (mainly ceftriaxone plus azithromycin) have been introduced in the United States  and Europe . No appropriate well-designed international study has yet assessed the implementation of dual antimicrobial therapy. However, as observed by the authors in many international projects the implementation of these guidelines appears suboptimal in several European countries and monotherapy with ceftriaxone remains frequently used.
No failure to treat urogenital gonorrhoea with ceftriaxone (250 mg–1 g) monotherapy has been verified to date. However, the observed initial accumulation of failures treating pharyngeal gonorrhoea was not unexpected, because these infections are substantially harder to eradicate with most antimicrobials than urogenital gonorrhoea [1-4,6,18]. As shown in the present study, ceftriaxone 500 mg monotherapy can be sufficient to eradicate urogenital gonorrhoea but not the concomitant pharyngeal gonorrhoea in the same patient. The pharyngeal gonorrhoea of the patients was instead successfully treated with 1 g ceftriaxone monotherapy or 250 mg ceftriaxone plus 1 g azithromycin. Unfortunately, 1 g ceftriaxone monotherapy may only provide a short-term solution [1,2,4,19,20] judging from the failure to treat the pharyngeal gonorrhoea caused by the first gonococcal XDR strain with 1 g ceftriaxone , ceftriaxone MICs of all the identified gonococcal XDR strains [9-11], emergence of ceftriaxone resistance and its anticipated trend, and pharmacodynamic/pharmacokinetic simulations showing that the benefits of increasing the ceftriaxone dose from 500 mg to 1 g are limited when taking into account the high ceftriaxone MICs detected recent years . Consequently, dual antimicrobial therapy, e.g. 500 mg ceftriaxone intramuscularly plus 2 g azithromycin orally, as recommended by the European gonorrhoea guideline , should ideally be implemented. It remains unknown if ceftriaxone and azithromycin act synergistically in vivo. However, most importantly, there are no indications, in vitro or in vivo, that they act antagonistically. According to a review from 2010, 99% of urogenital and 98% of pharyngeal gonorrhoea cases may be treatable with 2 g azithromycin monotherapy . Consequently, nearly all gonorrhoea cases (ceftriaxone-resistant or not) are treatable with even 2 g azithromycin monotherapy. Nevertheless, azithromycin monotherapy is not recommended due to the spread of gonococcal strains with high-level resistance to azithromycin and the anticipated rapid selection of azithromycin resistance [1,17,20].
All ceftriaxone treatment failures in the present study (Cases A, B and C) were caused by the internationally spreading multidrug-resistant gonococcal NG-MAST genogroup 1407 clone, which has caused many ESC treatment failures internationally [4-6,9,15]. However, the cefotaxime treatment failure was caused by the unrelated NG-MAST ST4539, which shows that clinical resistance to injectable ESCs is emerging also in other gonococcal clones.
In conclusion, increased awareness of treatment failures particularly with antimicrobial monotherapy, improved implementation of recommended dual antimicrobial therapy (e.g. 500 mg ceftriaxone plus 2 g azithromycin ), frequent test of cure (ideally for all cases, and at least for all cases of pharyngeal gonorrhoea), and appropriate verification/falsification of suspected treatment failures (including subsequent tracing of sexual contacts of the index case with the treatment failure) are essential internationally. An enhanced focus on pharyngeal gonorrhoea is also crucial, with increased sampling and prevention, e.g. promotion of condom use also when practising oral sex. Ultimately, novel options for effective treatment of gonorrhoea are imperative.
We are grateful to Pernilla Stocks Odebrant and Anna Wideskär-Benoni for providing clinical data.
Conflict of interest
MU, AKO, PL, TR, and HF designed and initiated this surveillance of treatment failures. DG, AKO, HJ, OE and MU performed and analysed all the laboratory work. PL, TR, HJ and OE collected clinical information. DG wrote the first draft of the paper and all co-authors were involved in finalising the paper.
*Erratum: The table was corrected and replaced on 12 August 2014.
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