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Volume 26-12 |
MASS TREATMENT/PROPHYLAXIS DURING AN OUTBREAK OF INFECTIOUS SYPHILIS IN VANCOUVER, BRITISH COLUMBIASyphilis is a sexually transmitted disease (STD) caused by the spirochete Treponema pallidum which is restricted to humans. Transmission occurs primarily during the infectious phase which consists of primary, secondary, and early latent syphilis. Primary syphilis is characterized by a painless ulcer approximately 3 weeks after exposure. Secondary syphilis is characterized by a generalized eruption 4 to 6 weeks after the primary stage in untreated patients. After weeks or several months, secondary manifestations resolve and about one-third of untreated cases become clinically latent sometimes leading to late manifestations involving the cardiovascular system, the central nervous system, skin, bones, and viscera. A diagnosis of early latent syphilis is made when the clinical situation and nontreponemal antibody titres reflect recent infection for which aggressive follow-up is necessary. Perinatal transmission can occur, especially during the infectious phase. The diagnosis of syphilis relies on clinical examination, darkfield demonstration of spirochetes in lesion exudate, non-specific treponemal antibody tests (rapid plasma reagin test and Venereal Disease Research Laboratory test), and specific treponemal antibody tests (microhemagglutination for Treponema pallidum and fluorescent treponemal antibody absorption test). The current treatment of choice is intramuscular benzathine penicillin G. Since July of 1997, British Columbia has experienced a serious outbreak of infectious syphilis. Overall rates have increased from 0.5/100,000 to > 3.0/100,000 with the downtown eastside (DTES) of Vancouver experiencing rates > 150/100,000 (Table 1). Annual cases have increased from 10 to 17 (1992-1996), to 46 (1997), 114 (1998), and 126 (1999) (Figure 1). A total of 273 cases have been reported in the 30 months since the outbreak began. Infectious cases by stage of disease are divided as follows: primary syphilis 31%, secondary syphilis 22%, early latent syphilis (duration < 1 year) 47%. Men account for 54% of cases. Age-adjusted rates are highest in men 30 to 49 years of age and women 20 to 39 years of age. The risk analysis shows that 42% of cases are related to the sex trade (24% sex trade clients, 18% sex trade workers), 13% are street involved (street kids and injection drug users), 16% report foreign exposure (Asia and Central America), 6% are gay males with anonymous sexual contacts, 14% report casual heterosexual contact, 7% are in other risk categories such as female spouses with only one sexual partner, and for 2% the risk is unknown. Many in the casual and street-involved risk categories are believed to be 'non-paying' sexual contacts of sex trade workers (e.g. pimps, pushers, and boyfriends). With this latter group, condoms are not often used. There were two cases of congenital syphilis in British Columbia in 1997. There has been no significant increase in late, non-infectious syphilis during this period. Table 1 Infectious syphilis by health region, 1998 (n = 112)
Figure 1 Cases of infectious syphilis by year, British Columbia, 1983-1999
Vancouver's DTES accounts for > 70 % of all cases in British Columbia (Table 1). The population of this area suffers from severe social problems including alcoholism and heavy injection drug use. The DTES has experienced successive epidemics of hepatitis B, drug overdose deaths, hepatitis C, HIV, and hepatitis A since the mid-1980s. Many of the cases in adjacent municipalities (Table 1) are sex trade clients. These clients have 'brought syphilis home' to unsuspecting wives in at least three instances. Caucasians account for 35% of cases, Aboriginals 22%, Asians 13%, Hispanics 8%, South Asians 6%, blacks 3%, and 14% are of unknown ethnicity. In the DTES, Aboriginals, Hispanics, and some Asian groups represent a much larger proportion of the population than they do in the rest of Vancouver and British Columbia. Half of the patients are diagnosed when they seek medical care because of acute symptoms, 12% are asymptomatic contacts to syphilis, and the rest are picked up through screening of one type or another (e.g. STD clinic patients, sex trade workers at drop-in support centres). Enhancement of standard public-health measures has not controlled the epidemic thus far. Intensive contact tracing, education of at-risk groups and physicians, increased diagnostic and treatment services, and intensified screening have been implemented for 24 months to no avail. Contact tracing has been especially difficult because of the lack of information on anonymous sexual contacts and sex trade contacts, and because of the 'code of silence' within this community. The mean number of contacts named per case is 1.5 and only 50% are successfully traced and treated. Sexual networks for the first 258 cases and contacts were predominantly singles (30), and dyads or triads (73). The three types of networks identified were (1) imported cases with secondary spread, (2) sex trade workers and clients, and (3) gay men with bathhouse contact. Concurrently, gonorrhea reached outbreak levels in British Columbia in 1999. There were 827 cases in that year compared to 546 in 1998 and 401 in 1997. An epidemiologic analysis of this outbreak is currently underway. There have also been small increases in reports of genital chlamydia infection in 1998 and 1999, but this may be due to the increased use of more sensitive diagnostic tests and/or the initiation of a province-wide chlamydia contact tracing program in 1998. Finally, there have been 15 new HIV infections in the last 24 months in men for whom sex trade worker contact has been the primary risk. There were no such cases in the 7 years before 1997. In an attempt to control the recent serious syphilis outbreak, the British Columbia Centre for Disease Control (BCCDC) implemented a mass treatment/prophylaxis program. During the weeks of 24 January and 21 February 2000, the STD/AIDS Division through its Street Nurse Program led an initiative to deliver > 7,000 treatment doses for syphilis to persons at risk in Vancouver's DTES, as well as key areas of risk activity in adjacent municipalities. The goal of the program was to treat as many persons at risk as possible over a short period of time. The program also included 'secondary carry' where participants were allowed to take treatment doses to others. Secondary carry targets were otherwise inaccessible core transmitter groups such as pushers, pimps, boyfriends, sex trade workers, and street kids who do not interact with outreach programs and who were therefore unlikely to participate in the mass treatment/prophylaxis program directly. Special sites ('john drop-ins') inside and outside of the DTES were established for 'no hassle' treatment of sex trade clients. To maximize coverage, only limited non-identifying information was obtained from participants and no specimens were collected. There have been two previous initiatives to control outbreaks of syphilis through mass treatment in North America; both using benzathine penicillin G, and both successful(1,2). Each of these initiatives was delivered on a smaller scale. Azithromycin dihydrate - 1.8 grams orally in a single dose - was used for British Columbia's syphilis mass treatment/prophylaxis initiative. Azithromycin dihydrate is approved for the treatment of gonorrhea and chlamydia; its effectiveness has recently been demonstrated in incubating syphilis(3) and infectious syphilis(4). It has also been shown to be effective against Ureaplasma urealyticum in vitro(5), and it is the current treatment of choice for Haemophilus ducreyi, the causative agent for chancroid(6). It has been successfully used in mass treatment programs for trachoma(7). It was part of the STD mass treatment study in Rakai, Uganda, where > 20,000 one-gram treatment doses were administered(8). There were very few side effects and no instances of anaphylaxis. Because of its long serum half-life and its concentration in tissues, the working hypothesis of this mass treatment/prophylaxis program was that temporary resistance would be established in the entire treated population, which in turn would prevent Treponema pallidum infection if exposure occurred. This prophylactic effect may be the primary factor in whether this initiative succeeded. Although incubating and infectious syphilis cases were undoubtedly be treated, the absolute numbers were likely small. The two rounds of treatment/prophylaxis were intended to cover the period of maximal infectiousness for syphilis. The rationales for this initiative can be summarized as follows:
A pilot study involving 23 participants and 108 secondary carries in November 1999 was successful without incident. After the initiative, a maintenance phase was instituted to consolidate any successes that are achieved. This phase includes enhanced outreach and contact tracing, intensive education and awareness programs, enhanced diagnostic and treatment services, intensified surveillance, Treponema pallidum DNA typing, and increased accessibility to the female condom. Sexually transmitted disease epidemics have been described as dynamic interactions among the pathogen, behavior, and prevention efforts which evolve through predictable phases(9). Within this model, one phase is low-level endemic transmission among core transmitter groups - which sustains the disease within an area and which is especially difficult to impact with traditional public-health control strategies. Outbreaks of endemic transmission may occur from time to time. One strategy which might be useful to deal with both the outbreaks during this phase and endemic transmission itself is mass treatment/prophylaxis. This strategy, however, is not often considered to be feasible and only rarely attempted. As public-health authorities in many countries consider elimination of STDs, especially syphilis, it will be necessary to consider strategies, both old and new, to deal with epidemics such as Vancouver's current syphilis outbreak. The mass treatment/prophylaxis that has been implemented in Vancouver's DTES may point to new directions in our public-health approach to STDs. References
Source: M Rekart, MD, STD/AIDS Control, D Patrick, MD, Communicable Disease Epidemiology, BCCDC, Vancouver, B.C.; A Jolly, PhD, T Wong, MD, Laboratory Centre for Disease Control, Health Canada, Ottawa, Ont.; M Morshed, PhD, Vector Borne Diseases and Non Viral Serology, Laboratory Services, H Jones, MD, C Montgomery, MD, L Knowles, BScN, N Chakraborty, BScN, J Maginley, BScN, STD/AIDS Control, BCCDC, Vancouver, B.C.
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Last Updated: 2002-11-08 |  |
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