To further characterize the CipR isolates, Lip subtyping was performed. A total of 9 different subtypes were seen, with 16b being the most prominent; it was found in 3 different A/S classes. The Lip subtyping also identified a group of CipR isolates that consisted of 12 strains (2 from 1998 and 10 from 1999) that had the same A/S class (Proto IB-10), GyrA/ParC alterations (91,95/Asp-86), and Lip type (16b). However, when the penicillin–tetracycline phenotypes of the isolates were examined, eight of the isolates were penicillinase-producing N gonorrhoeae (PPNG), three were chromosomally resistant N gonorrhoeae (CMRNG), and one was penicillinase-producing/plasmid-mediated tetracycline-resistant N gonorrhoeae (PP/TR).
Among the CipR isolates were six sets (five pairs and one triplet) of isolates from patients who were culture-positive on their follow-up visit to the clinic. These sets were examined by A/S classification, Lip subtype, GyrA/ParC alterations, and penicillin/tetracycline susceptibilities. In four of the sets (Table 3, patients 1, 3, 4, and 5), the pretreatment and posttreatment isolate pairs had identical strain phenotypes. The other two sets, patients 2 and 6, had identical A/S class, GyrA/ParC alterations, and Lip subtype but differed in their penicillin–tetracycline phenotype. Patient 2’s initial isolate was CMRNG, and the follow-up isolate was PPNG. Patient 6 had 3 isolates; the first 2 isolates were PPNG and the third isolate was PP/TR.
Resistance to ciprofloxacin has increased dramatically since 1994–1995, when only one CipR isolate was detected among a total of 101 isolates. 25 In 1998–1999, decreased susceptibility to ciprofloxacin occurred in a large variety of strains as defined by A/S class, Lip subtype, and GyrA/ParC alterations. After initial examination of the results, there appeared to be two strain clusters of CipR isolates, on the basis of A/S class, that contained four or more isolates. In 1998, a cluster of four Pro/IB-3 CipR isolates was present. However, GyrA/ParC alteration analysis revealed that two of the isolates were 91,95/none and two isolates were 91,95/Ser-87. In 1999, a cluster of 10 Proto IB-10/Lip 16b/91,95/Asp-86 CipR isolates appeared. However, upon examination of the isolates’ penicillin–tetracycline phenotype, eight isolates were found to be PPNG, three were CMR, and one was PP/TR. The presence of the possible strain clusters reinforces the need to use multiple methods when subtyping N gonorrhoeae.
The sets of isolates from the six patients who had positive cultures at the follow-up visit appear to represent varying scenarios. The CipR isolates from patients 3, 4, and 5 appear to represent treatment failures, in that all 3 patients were treated with ciprofloxacin and the dates of their follow-up cultures were in the 7 to 10–day range, which would be consistent with treatment failure. Isolates from patient 1 could also represent a treatment failure since both isolates possess the same strain phenotype, but no treatment data were available for this patient. Isolates from patient 2 appear to indicate a reinfection since the original and posttreatment isolates have different penicillin–tetracycline phenotypes, the patient was treated with ceftriaxone, and the initial isolate was susceptible to this drug. The time period between the initial and follow-up culture, 30 days, would also be consistent with the opportunity for reinfection. Patient 6 had 3 isolates cultured, the first 2 of which had the same strain phenotype. However, the patient was treated with doxycycline, so this could not be considered a ciprofloxacin treatment failure. The third isolate appears to be the result of a reinfection, because this isolate was PP/TR, which contrasts with the first and second isolates, which were PPNG.
The epidemiology of gonorrhea in Thailand has changed dramatically in recent years. Reported cases decreased from 227,451 in 1985 to only 5,382 in 1999, a 42-fold decline. 26 This decline was likely due to decreases in commercial sex patronage and increases in condom use during commercial sex in response to the HIV/AIDS epidemic in Thailand. 27 The wide availability of single-dose, oral treatment of urethritis with fluoroquinolones may also have contributed to the decrease in reported cases. From 1999 to 2000, cases increased 4.5% to 5,622. 26 This increase is likely to be due in part to the emergence of gonococcal resistance to fluoroquinolones as described here, although behavioral changes, including an increase in casual, noncommercial sex, may also have had a role. 28
In summary, these results strongly suggest that the continuing emergence of CipR gonococci is not due to expansion of a single or a few strains but to the emergence of many different CipR gonococcal strains that continue to spread. The importation of CipR strains from other Asian countries and de novo generation of ciprofloxacin resistance in endemic ciprofloxacin-susceptible strains may also have contributed to the increase in CipR isolates in the 1990s. Because of this high level of CipR isolates at Bangrak Hospital, in 2000 the Thai Ministry of Public Health recommended not using fluoroquinolones for the treatment of gonococcal infection in Thailand. Furthermore, the emergence of additional isolates with high ciprofloxacin MICs illustrates the need for continued monitoring throughout the world of the susceptibilities of N gonorrhoeae isolates to fluoroquinolones.
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