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  2005

Epidemiologic 

Report

Antibiotic sensitivity of Neisseria gonorrhoeae isolates in South Australia in 1999.

Increasing antibiotic resistance of bacteria is of concern in the control of sexually transmitted diseases. In Australia, gonococcal isolates are routinely monitored for antibiotic susceptibility in the laboratory. This article describes South Australian links between emerging patterns of resistance and epidemiologic information.

The capacity of Neisseria gonorrhoeae to develop resistance to antimicrobial agents used for the treatment of gonorrhoea is well known. In Australia, the progressive emergence and spread of antibiotic resistant gonococci has been observed, and, in some countries near Australia, high proportions of gonococcal isolates are resistant to several antibiotics.¹

The antibiotic susceptibility of Neisseria gonorrhoeae in Australia is monitored by the Australian Gonococcal Surveillance Programme (AGSP) which is a collaborative programme conducted by reference laboratories in each State and Territory. The South Australian reference laboratory is the Infectious Diseases Laboratories of the Institute of Medical and Veterinary Science (IMVS). All isolates of Neisseria gonorrhoeae are examined for susceptibility to penicillin (representing this group of antibiotics), ceftriaxone (representing later generation cephalosporins), ciprofloxacin (representing quinolones), spectinomycin, and high level resistance to tetracycline.¹

In 1999, 243 cases of sexually transmitted gonorrhoea were notified in South Australia. Whilst Neisseria gonorrhoeae was isolated from 129 of these cases (53%), 84 viable samples were received by the IMVS for further testing. Hence, antibiotic sensitivity results were notified to STD Services for 84 (65%) of the 129 cases. The remaining 114 cases (47%) were diagnosed by polymerase chain reaction testing (PCR) of, predominantly, urine samples submitted from remote communities where annual screening programs have been implemented.

Antibiotic Susceptibility Results

During 1999, 84 viable specimens were available for standardised testing against a panel of antibiotics used for the treatment of gonorrhoea; these data were then analysed, correlating isolate results to medical notification information.

Penicillins

In 1999, 66 (78%) cases were classified as sensitive to penicillin (Table 1). However only four cases (4%) were fully sensitive (minimum inhibition concentration - MIC £ 0.008-0.03ug/ml), with 62 cases (74%) being less sensitive (MIC 0.06-0.5ug/ml) to penicillin.

Resistance to the penicillin group (penicillin, ampicillin, amoxycillin) may be mediated by the production of beta-lactamase (penicillinase-producing N. gonorrhoeae – PPNG) or by chromosomally-controlled mechanisms (CMRNG).^1,2

Eighteen cases (22%) showed resistance to penicillin, including three cases (4%) of PPNG (Table 1). This incidence of PPNG was within the range (0-12%) occurring in the years from 1984 to 1998.³

All three PPNG cases (one female, two males) were Caucasians who acquired the infection in South Australia. Male-to-male sex was reported for one case. Nationally from 1998 to 1999, the AGSP recorded an increase in PPNG from 5.3% to 7.4% of all isolates, with New South Wales (NSW) and Western Australia (WA) recording 9.7% and 9.6% PPNG, respectively.¹

Since 1995, an increase in chromosomal mediated resistance (CMR) to penicillin has been observed in South Australia.³ During 1999, 15 cases (18%) demonstrated CMR. Fourteen cases were male and one female; ten of the fourteen males reported male-to-male sex. Eleven cases were acquired in South Australia (predominantly in urban areas), two were acquired interstate and two overseas. Thirteen cases were Caucasian, one case was Aboriginal and one case was Asian. Nationally the AGSP recorded a fall in CMR from 21.8% to 14.3% of isolates between 1998 and 1999. The proportion of CMR varied amongst states with South Australia (18%) and NSW (24.6%) recording high levels of CMR and WA (2%) and Northern Territory (1.6%) recording low levels.¹

Ceftriaxone and Spectinomycin

Both in South Australia and nationally, all isolates were sensitive to Ceftriaxone and Spectinomycin.¹

Ciprofloxacin

Eighty two cases (98%) were sensitive to Ciprofloxacin and two cases (2%) were resistant (Quinolone resistant N. gonorrhoeae - QRNG) (Table 1). Both cases of QRNG, one male and one female, were Caucasian and acquired their infections in South Australia. Nationally, the AGSP noted a rise in QRNG between 1998 and 1999 from 5.2% to 17.2% of isolates. The number of QRNG isolates observed in Australia in 1999 (628) was more than three times the 186 isolates noted in 1998, with 90% of 1999 QRNG isolates reported from NSW or Victoria.¹

Tetracycline

In South Australia, gonococcal isolates are tested at a single concentration of tetracycline (16mg/ml) to measure high level resistance. Eighty isolates (95%) were not tetracycline resistant N. gonorrhoeae (not-TRNG) at this level, and four isolates (5%) were resistant (TRNG) (Table 1). Three males, with female partners, acquired the infection in Indonesia; and one female acquired the infection in South Australia from a partner who had been infected overseas. Nationally, 7.9% of isolates in 1999 were TRNG, with most cases being acquired overseas.¹

Table 1 Antibiotic sensitivity for South Australian Cases of gonorrhoea 
             isolated in 1999.

Antibiotic Treatment

In South Australia the continued surveillance and monitoring of gonococcal isolates led to altered treatment regimes for gonorrhoea in June 1998. Intramuscular ceftriaxone (250mg) is the drug of choice for gonorrhoea. Ciprofloxacin (500mg oral stat) is a useful alternative if there is no history of interstate or overseas travel in the last 3 months. Amoxycillin (3 grams) with probenicid (1 gram) is no longer considered effective therapy for infections acquired in the metropolitan area. Treatment options for infections acquired in remote or rural Australia should be discussed with a consultant sexual health physician or infectious disease physician.

It is recommended that patients be re-tested for gonorrhoea five to ten days after antibiotic treatment to ensure that the medication has been effective. The STD Services publication "Diagnosis and Management of STDs", fifth edition, 2000 contains more detailed information on management and treatment of gonorrhoea and is available on the STD services website, or, directly from STD Services.^{4, 5}

Acknowledgments

STD Services would like to thank the IMVS, in particular, Lance Mickan and Rachael Pratt, for providing the antibiotic sensitivity results for South Australian cases of gonorrhoea.

References

1. Australian Gonococcal Surveillance Programme. Annual report of the Australian Gonococcal Surveillance Programme, 1999. CDI 2000;24:113-117.
2. Holmes K.K et al. Sexually Transmitted Diseases, Third edition. McGraw-Hill, 1999
   p 444.
3. Sexually Transmitted Diseases Services, South Australia. Sexually Transmitted Diseases in South Australia - Epidemiological Report Number 13, 1999. Royal Adelaide Hospital, South Australia 2000 pp 12-15..
4. Sexually Transmitted Diseases Services, South Australia. Diagnosis and Management of STDs (including HIV infection). Fifth edition, Royal Adelaide Hospital, South Australia, 2000.
5. stdservices@dhs.sa.gov.au 

Bernadette Kenny
Surveillance
STD Services
August 2000

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