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Epidemiologic Notes and Reports Multiple Strain Outbreak of Penicillinase-Producing Neisseria gonorrhoeae -- Denver, Colorado, 1986

In 1986, the Denver Metro Health Clinic (DMHC) detected 40 cases of infection with strains of penicillinase-producing Neisseria gonorrhoeae (PPNG). This was a marked increase over the nine cases* found during the preceding 5 years. The increase in cases began during the last 2 months of 1985, when three cases were detected. From January through May 1986, seven additional cases were identified.** Beginning on June 2, 1986, all isolates were routinely screened for |gb-lactamase, and, over the next 7 months, 33 of 1,358 isolates (2%) were identified as PPNG strains. Four of these occurred among persons referred to the clinic as known sexual contacts of PPNG- positive patients. One was from a patient with possible treatment failure, and 28 were from patients not suspected of infection with PPNG.

The epidemic peaked during the period from August through November (Figure 1). Since the DMHC treats over 50% of all reported cases of gonorrhea in the city and county of Denver, trends among patients in these clinics are considered representative of trends in the greater Denver metropolitan area. On August 18, 1986, the Colorado Department of Health issued an advisory requesting other Denver metropolitan laboratories to begin routinely screening all isolates for b-lactamase. They also recommended treating patients with confirmed or suspected cases of PPNG infection with ceftriaxone or spectinomycin. Because of the persistence of the outbreak, the Denver Disease Control Service issued an advisory for metropolitan Denver in November, reiterating the need for therapy effective against PPNG for all patients with PPNG infection, their sexual partners, and any patient who might be unlikely to comply with tetracycline therapy.

The 40 cases of PPNG occurred among 39 patients (one woman appeared to be re-infected approximately 1 month after her initial treatment). Twenty-four patients (62%) were men, 21 of whom were heterosexual. Twenty-two (92%) of the 24 men had symptoms of discharge or dysuria; 12 (80%) of the 15 women also had symptoms of discharge. Results of post-treatment cultures were available for 18 (45%) of the 40 patients. All 18 were culture-negative, comprising six treated with spectinomycin, eight treated with both spectinomycin and tetracycline, and four treated with tetracycline alone.

Thirty-two (82%) of 39 patients (14 women and 18 men) were interviewed by disease-intervention specialists from the Colorado Department of Health. Four (29%) of 14 women gave a history of prostitution, and five (28%) of 18 men gave a history of contact with prostitutes. Nine (28%) of 32 patients gave histories suggesting that they may have become infected outside of Colorado.*** The 32 patients named 76 sexual contacts, 49 (64%) of whom were traced and evaluated. Sixteen of the contacts were culture-positive, and 14 (88%) of these had PPNG strains. The other 33 (67%) of the 49 contacts were culture-negative for N. gonorrhoeae and received treatment with either spectinomycin or ceftriaxone.

The minimum inhibitory concentrations (MICs) of penicillin, tetracycline, and spectinomycin were determined for 38 of 40 isolates by an agar dilution method. The geometric mean MICs for tetracycline and spectinomycin in the 1986 PPNG isolates were similar to those for isolates from systematically selected patients seen from 1981 through 1986. However, the 1986 PPNG isolates had lower geometric mean MICs for tetracycline than did isolates from patients with treatment failure from 1981 through 1986 (0.67 compared with 3.03mg/ml). All isolates tested were susceptible to spectinomycin (MIC less than 64mg/ml).

Auxotype/serovar and plasmid analysis of 36 of the 40 PPNG isolates from 1986 has been completed. Eight auxotype/serovar classes were involved in the outbreak. Four auxotype/serovar classes were represented by isolates from at least five individuals. Plasmid analysis indicates that all isolates contained either the 3.2 (44%) or 4.4 (56%) Mdal plasmid for b-lactamase production, but only those from one class (Proto/IB-3) contained the 24.5 Mdal conjugative plasmid. Reported by: J Douglas, MD, F Judson, MD, Denver Disease Control Svc, Denver; N Spencer, R Hoffman, MD, State Epidemiologist, Colorado Dept of Health. Sexually Transmitted Diseases Laboratory Program, Center for Infectious Diseases; Div of Sexually Transmitted Diseases, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Although the incidence of PPNG has been concentrated in New York, California, and Florida, outbreaks in other parts of the country are occurring frequently (1). The absence of PPNG strains among the systematically selected isolates screened in the previous 5 years at the DMHC suggests that the increase in cases reflected a new problem and was not due solely to screening. A high proportion of patients in the Denver outbreak gave histories suggesting that they may have become infected outside of Colorado and/or may have been involved in prostitution-related activities. These histories, along with the diversity of auxotype/serovar classes involved and the presence of both the 3.2 Mdal and 4.4 Mdal b-lactamase plasmids among the isolates, strongly suggest that this outbreak is in reality a series of "mini-outbreaks" caused by different strains of PPNG.

In contrast to previously reported experiences in the United States (2-4), the Denver PPNG isolates were relatively susceptible to tetracycline. This pattern reflects the high proportion of strains with the 3.2 Mdal plasmid, which is characteristically associated with increased tetracycline susceptibility. The DMHC's routine use of tetracycline in treating heterosexuals with gonorrhea probably delayed recognition of the onset of the outbreak, as evidenced by the increase in incidence of PPNG cases after the institution of routine screening of all pretreatment isolates for b-lactamase.

CDC currently recommends that all gonococcal isolates be tested for b-lactamase production. In areas where the proportion of gonococcal disease caused by PPNG strains is greater than 1%, all patients diagnosed with gonorrhea should be treated with a regimen effective for antimicrobial-resistant gonorrhea (e.g., ceftriaxone, 250 mg, intramuscularly). In addition, patients treated for gonorrhea should receive 1 week of tetracycline or erythromycin therapy for the cotreatment of chlamydial infection (5). Detailed guidelines for the diagnosis, therapy, and recommended public health interventions for antimicrobial-resistant gonococcal infections will be published as an MMWR supplement in September.


  1. CDC. Penicillinase-producing Neisseria gonorrhoeae -- United States, 1986. MMWR 1987; 36:107-8.

  2. Perine PL, Schalla W, Siegel MS, et al. Evidence for two distinct types of penicillinase- producing Neisseria gonorrhoeae. Lancet 1977;2:993-5.

  3. Siegel MS, Thornsberry C, Biddle JW, O'Mara PR, Perine PL, Wiesner PJ. Penicillinase- producing Neisseria gonorrhoeae: results of surveillance in the United States. J Infect Dis 1978;137:170-5.

  4. Jaffe HW, Biddle JW, Johnson SR, Wiesner PJ. Infections due to penicillinase-producing Neisseria gonorrhoeae in the United States: 1976-1980. J Infect Dis 1981;144:191-7.

  5. CDC. 1985 STD treatment guidelines. MMWR 1985;34(4S). *These nine strains were found among 549 isolates from patients with treatment failures. No strains of PPNG were found among the 789 isolates from systematically selected patients. **Five were found by routine screening of systematically selected isolates, and two were from patients referred to DMHC as sexual contacts of patients with confirmed cases of PPNG infection. ***California, four cases; Nebraska, Florida, Tennessee, Michigan, and Thailand one case each.

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