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Journal of Clinical Microbiology, August 2008, p. 2731-2738, Vol. 46, No. 8
0095-1137/08/$08.00+0 doi:10.1128/JCM.00228-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Infectious Disease Section, Department of Medicine, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire,1 Department of Medical Microbiology and Immunology, Creighton University School of Medicine, Omaha, Nebraska,2 Procter & Gamble, Cincinnati, Ohio,3 Procter and Gamble Far East, Kobe, Japan,4 Department of Infectious Diseases, Tokyo Women's Medical University School of Medicine, Tokyo, Japan5
Received 4 February 2008/ Returned for modification 5 May 2008/ Accepted 30 May 2008
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mTSS among women in Japan appears to be rare, with approximately 12 cases reported in the literature; however, to the best of our knowledge, there have been no formal studies of the true incidence of mTSS in Japan. There have been numerous reports, however, of neonatal TSS-like exanthematous disease (NTED), which is typically characterized by fever, erythema, and thrombocytopenia (49). Most reported cases of NTED have been caused by TSST-1-producing, methicillin-resistant strains of Staphylococcus aureus (MRSA) (22, 29, 32, 33), and susceptibility to this toxin was indicated by low levels of antibody directed against TSST-1 (32).
The development of mTSS requires vaginal colonization or infection with a toxin-producing strain of S. aureus in the absence of positive antibody (titer of
1:32) against the toxin. Previous studies have reported vaginal colonization rates for toxigenic S. aureus ranging between 1 and 4% (4, 24, 36, 39). A positive titer of serum antibody to TSST-1 has been shown to be common, generally on the order of 80 to 90%, among healthy adults from multiple countries in North America, Europe, and Asia (8, 10, 25, 43; J. Seymour, presented at Unresolved Infectious Disease Issues in Obstetrics and Gynecology: an International Symposium, New York, NY, 2002). TSST-1-producing strains in the United States have generally been methicillin susceptible, but cases of mTSS caused by MRSA have been reported in the United States (27) and elsewhere (6, 13).
We undertook the current study to determine the prevalence of microbiologic and immunologic risk factors for mTSS among Japanese women, as well as the relationship between toxin production and other molecular characteristics, such as those coding for methicillin resistance.
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(ii) U.S. control subjects. Healthy, menstruating, and ethnically Japanese and Caucasian women in the same age range and with the same age distribution as the Tokyo subjects were recruited from Long Beach and Costa Mesa, CA, and the surrounding area by West Coast Clinical Trials, Inc. The Caucasian control subject group consisted of non-Hispanic women matched in age (± 2 years) to the Japanese study subjects. U.S. control subjects were eligible for enrollment if they were born in the United States, had regular menstrual cycles, had not recently used immunosuppressive drugs or had been diagnosed as having an immunosuppressive disease, and had not resided outside the continental United States or Canada for more than 5 years.
Written, informed consent was obtained from the subjects prior to the collection of any information or clinical samplings. Subjects were removed from the study if they failed to meet the inclusion criteria or satisfied any of the exclusion criteria at any time during the study.
Conduct of study. In Japan, the study was conducted from 10 March 2005 through 28 March 2005. In the United States, the study was conducted from 30 December 2005 through 15 May 2006. The protocol and informed consent documents were reviewed and approved by an ethics committee or institutional review board, as appropriate, in both locations.
Demographics, habits and practices, and medical history questionnaires. The subjects in both study groups were asked to answer questions regarding demographic characteristics, specific hygiene habits and practices, and medical history, including the use of feminine hygiene products, birth control methods, sexual activity, pregnancies, vaginal infections, vaginal discharge, and menstruation history. In addition, U.S. Japanese subjects were asked whether they lived a traditional Japanese lifestyle or a Western lifestyle.
Sample collection. Samples for both microbiologic and immunologic analyses were collected from the subjects in Japan, while samples for immunologic analysis only were collected from the U.S. subjects. In both locations, blood samples for immunologic analysis were collected upon entry into the study. For Tokyo subjects only, the anterior nares were swabbed at a penetration of 1 to 2 cm. Throat samples were obtained by swabbing the area of the tonsillar fauces. Vaginal samples were obtained by inserting a swab into the vagina (without using a speculum) and swabbing the mid-upper vaginal walls approximately 5 cm past the introitus. The labia were spread during this procedure to minimize the potential for contamination by perineal flora.
Sample handling. Serum samples from the Japanese subjects were frozen and shipped on dry ice within 96 h to Dartmouth-Hitchcock Medical Center (Lebanon, NH) for analysis of TSST-1 immunoglobulin G antibodies. The nasal, throat, and vaginal swabs collected in Japan were refrigerated upon collection and delivered within 24 h to SBS Laboratory (Kanagawa, Japan) for the isolation of S. aureus. Isolates of S. aureus were streaked onto Trypticase soy agar slants for shipment to Creighton University School of Medicine (Omaha, NE) and analyzed for the presence of tst, as well as the presence of mecA and the genetic relatedness of TSST-1-producing isolates. Isolates were also shipped to Dartmouth-Hitchcock Medical Center for analysis of the production of TSST-1 and for antibiotic susceptibility testing. Serum samples from the U.S. subjects were similarly stored, frozen, and shipped to Dartmouth-Hitchcock Medical Center for TSST-1 antibody analysis.
Analyses of sera for anti-TSST-1.
A sandwich enzyme-linked immunosorbent assay was used to measure human TSST-1 immunoglobulin G antibodies, as described previously (36). Nonimmune sera from healthy volunteers and commercially available human immunoglobulin (Sandoglobulin; Sandoz Pharmaceutical Company, East Hanover, NJ) served as negative and positive controls, respectively. Samples with titers of
1:4 were classified as negative for antibody, whereas those with titers of
1:32 were classified as positive; those with titers of 1:8 and 1:16 were classified as intermediate.
Analyses of S. aureus isolates. The vaginal, nasal, and throat swabs from each Japanese subject were streaked for isolation onto mannitol salt agar plates (PML Microbiologicals, Mississauga, Ontario, Canada). The plates were incubated at 36°C for 48 h in 5% CO2. The vaginal swabs were also incubated overnight in brain heart infusion broth supplemented with polymyxin B (10 µg/ml) and nalidixic acid (10 µg/ml) for the enhancement of S. aureus, followed by streaking onto blood agar plates. After incubation, the plates were examined for the characteristic morphology of S. aureus, and suspicious colonies were subcultured onto tryptic soy agar plates with 5% sheep blood (PML Microbiologicals) and incubated for 24 h. Gram stain, catalase, and tube coagulase tests were performed to confirm the identification of S. aureus.
Cell supernatants from positively identified S. aureus isolates were analyzed in a competitive enzyme-linked immunosorbent assay for TSST-1 (38). S. aureus strains MN8 and ATCC 25923 were used as positive and negative controls, respectively.
The methicillin resistance of TSST-1-producing S. aureus isolates was determined by means of an oxacillin agar screening test (MRSA screening agar; Remel, Lenexa, KS) (5). The control strains of S. aureus included ATCC 25293, a penicillin-sensitive strain; ATCC 43300, a MRSA strain; and MN8, a penicillin-resistant, mTSS-associated strain.
Molecular analysis of S. aureus isolates. Isolates were screened by Southern hybridization (46) for the presence of tst and mecA genes by PCR amplification of probes from S. aureus MN8 and S. aureus EMRSA16, respectively, using digoxigenin-labeled dideoxy-UTP (Roche, Indianapolis, IN). The primers and PCR conditions used to amplify both mecA and tst have been previously described (12, 28). In methicillin-resistant isolates, typing of the staphylococcal chromosomal cassette mec (SCCmec) was performed as described by Oliveira and de Lencastre (34). Multilocus sequence typing (MLST) was performed using the PCR primers and amplification conditions described by Enright et al. (11).
For S. aureus isolates producing TSST-1, molecular strain typing to assess genetic relatedness was performed by pulsed-field gel electrophoresis (PFGE) as previously described (15). The resulting pulsed-field types of isolates were categorized based on criteria established by the CDC (26).
Statistical analyses. Data from the Tokyo subjects were analyzed by logistic regression using the GENMOD procedure in SAS release version 8 (47), both with and without age included as a continuous covariate, to examine the association of demographic, medical history, and habits and practices data with the presence of TSST-1-producing S. aureus and the prevalence of positive antibody titers. To compare groups (or subgroups) for the prevalence of positive antibody titers, a series of two-way logistic regression models was run with a subject characteristic variable included as a factor and age included as a covariate. A separate logistic model included only group (or subgroup) and age. To further examine the correlation between ordinal variables and the prevalence of positive antibody titers, Cochran-Mantel-Haenszel chi-square tests (47) were also conducted within groups (or subgroups) using the FREQ procedure in SAS. All data except for the data from one subject in the U.S. study who was inappropriately enrolled were included in the statistical analysis. Statistical significance was declared at the two-sided 0.05 significance level.
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TABLE 1. Age distribution and antibody status among subjects
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1:32) among the Japanese (Tokyo) subjects was 47% (98 of 209 subjects). The prevalence of positive titers of antibody to TSST-1 exhibited a statistically significant association with older age (P = 0.002) (Fig. 1). Subjects colonized in the nose and throat with toxigenic S. aureus had higher antibody titers than those colonized in the vagina (Table 2). Out of the 12 subjects colonized with the TSST-1-positive strain, only one subject lacked a positive antibody titer. This one subject was colonized vaginally.
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FIG. 1. Logistic regression results: the probability of being seropositive for anti-TSST-1 antibodies versus the age of Japanese women in Tokyo and control women of Caucasian and Japanese ancestry in the United States. P values for age were 0.002 (Japanese women in Tokyo), 0.315 (Japanese women in the United States), and 0.465 (Caucasian women in the United States).
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TABLE 2. Characterization of Japanese women with TSST-1-producing S. aureus colonizationa
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(iii) Japanese subjects and U.S. control groups.
Caucasian subjects had a significantly higher prevalence of positive antibody titers (P
0.004) than Japanese subjects in Tokyo or the United States. U.S. Japanese subjects also had a significantly higher prevalence (P < 0.001) of positive antibody titers than Tokyo Japanese subjects. Figure 2 depicts the antibody titer distribution for all subjects. Only 12 of 137 Caucasian subjects (9%) had little or no detectable antibody (titer
1:4), compared with 90 of 209 Tokyo Japanese subjects (43%) and 30 of 133 U.S. Japanese subjects (23%).
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FIG. 2. Titers of anti-TSST-1 antibodies in Japanese women in Tokyo and in control women of Caucasian and Japanese ancestry living in the United States.
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TABLE 3. S. aureus and TSST-1-producing S. aureus colonization results for Tokyo Japanese subjectsa
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FIG. 3. PFGE macrorestriction analysis of the 14 TSST-1-producing isolates cultured during the study. Angle brackets indicate isolates with indistinguishable PFGE patterns from the same subject. Methicillin-resistant isolates are indicated by an asterisk.
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(ii) U.S. control groups. Caucasian subjects had a significantly higher prevalence of positive antibody titers than Japanese subjects living in self-declared traditional Japanese households (P = 0.002) and a higher (approaching statistical significance) prevalence of positive antibody titers than Japanese subjects living in nontraditional Japanese households (P = 0.065). There was a significant association between the prevalence of positive antibody titers to TSST-1 and the number of sexual partners within the year prior to the study (P = 0.0048). Only 59% (13 of 22) of U.S. Japanese subjects with no sexual partners in the year prior to the study had positive antibody titers, compared with 78% (75 of 96) of those reporting one sexual partner and 86% (12 of 14) of those with at least two sexual partners over this period. For all U.S. Japanese subjects, the prevalence of positive antibody titers was not influenced by history of tampon use, sexual intercourse, or pregnancy. Japanese tampon users from nontraditional households were not significantly different from Caucasians with respect to the prevalence of antibody.
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In contrast, there have been approximately 12 well-documented cases of mTSS in Japan over the past 15 years (2, 19, 20, 23, 31, 35, 45, 50), despite the fact that TSST-1-producing strains of S. aureus are prevalent throughout the country (18, 52, 53). It is unclear whether the small number of reported mTSS cases reflects the failure to recognize the disease, underreporting of the disease, or a rate that is actually lower than that in the United States because of microbiologic or immunologic reasons.
The global incidence of TSST-1-producing strains has been documented worldwide (Seymour, unpublished report). Colonization with S. aureus is generally highest (20 to 30%) in the nose or oropharynx among non-health-care workers (36). Vaginal colonization with S. aureus has been determined to be lower (10% to 20%) in the United States, Europe, and Asia (36; Seymour, unpublished report). Similarly, TSST-1-producing strains of S. aureus have been isolated vaginally from 1 to 4% of healthy, menstruating women in the general population (1, 4, 24, 36, 39). Reports from Japan over the past few years have shown TSST-1 to be responsible for a large number of NTED cases, a disease of neonates that lack maternal antibody to the toxin. In this light, the relative infrequency of mTSS in Japan is especially striking (22, 29, 48, 49).
The purpose of this study was to obtain additional information regarding microbiologic and immunologic risk factors related to mTSS. The study enrolled 209 healthy adult women in Tokyo and included collection of demographic and health practices information, sera for antibody testing, and samples from three mucosal sites for isolation of S. aureus; we characterized the staphylococcal isolates for the production of TSST-1, methicillin resistance, and additional molecular characteristics. Our key finding, with respect to antibody, was that only 47% of women had positive titers of anti-TSST-1 antibody, a rate that was significantly lower than the reported seropositivity rates in the United States and Europe (36). After the data were corrected for age, there were no significant predictors of the presence of antibody to TSST-1.
Because of the lower than expected seropositivity rate for TSST-1 among Japanese women, we conducted a follow-up study in the United States aimed at elucidating the extent to which genetics and environmental factors influenced the development of antibody. As a group, U.S. women had a high rate of seropositivity for TSST-1 (82%) (P < 0.001 versus women in Japan), which was comparable to the rate found in a large study previously conducted in the United States (36).
Of interest, however, was that ethnic Japanese women living in the United States had a seropositivity rate (75%) that was significantly higher than that of Japanese women living in Tokyo (47%), suggesting a strong environmental influence on the development of antibody, but also had a lower rate than that of a cohort of Caucasian subjects (89%). In the larger previously conducted U.S. study, the black population demonstrated a 78% positive antibody titer level (36). The black population in the United States does not appear to be at an increased risk for mTSS based on the reported incidence rates (3, 16).
The difference between Japanese-American and Caucasian subjects is most likely a reflection of differences in lifestyle and health practices. Japanese-American women who described themselves as living in traditional Japanese households were less likely to have positive antibody titers than those who had assumed a Western lifestyle. A history of recent sexual intercourse was associated with a higher rate of seropositivity among Japanese-American women, as was tampon use among Japanese-American women living in nontraditional households. These results, taken together, suggest that the development of antibody to TSST-1 is largely, if not exclusively, a function of environmental factors rather than a genetic inability to develop antibody. For example, while tampons are not a source of S. aureus (44), digital procedures associated with the insertion of tampons and barrier contraceptives may increase the potential exposure to S. aureus, resulting in vaginal colonization.
The relatively low rate of seropositivity for TSST-1 in Japan was not a result of lack of colonization by S. aureus and specifically by TSST-1-producing strains: 52% of women were colonized with S. aureus at one or more mucosal sites (Table 2), 8.8% of all isolates produced TSST-1, and 6% of women were colonized with a TSST-1-producing strain. Two of the 209 women (0.9%) had TSST-1-producing S. aureus vaginal colonization, which is similar to the rate found in other geographical locations (1, 4, 24, 36, 39). Colonization with a toxin-producing strain was associated with a high rate of antibody positivity: 92% of women colonized with a toxin-producing strain had a high level of antibody (Fig. 4). Subjects with nose and/or throat colonization with a toxin-producing strain had higher antibody titers than those with vaginal colonization (Table 3). It has been demonstrated that nasal exposure to superantigens (e.g., TSST-1) is an excellent avenue for generating neutralizing antibodies to superantigens and for enhancing the bactericidal activity of neutrophils (30). Furthermore, the nasal mucosae consist of a thin, pseudostratified, columnar epithelium interspersed with glandular ducts and resting on a basement membrane. This nasal basement membrane is semipermeable due to capillary penetration, which makes it fundamentally different from basement membranes found elsewhere in the human body (54). One could speculate that the nasal basement membrane of the throat and nasal mucosal surfaces may be easier for toxin to penetrate than the more robust barrier of the vagina (7, 42). These differences may warrant further investigation of this hypothesis. It was noted that nasal colonization with toxigenic S. aureus was 6% in North America (36) and 3% in Japan (chi-square P value, 0.0695), which suggests a trend, although not statistically significant, toward higher colonization and potential exposure to the toxin via the nose in North American women versus the study population.
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FIG. 4. Titers of anti-TSST-1 antibodies in Japanese women in Tokyo and Japanese women colonized with TSST-1-producing S. aureus.
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The low rate of seropositivity seen in the Tokyo Japanese women was unexpected. Since 92% of the Tokyo Japanese subjects who carried a TSST-1 strain had positive antibody titers, either exposure to the toxin is limited, Japanese women are genetically nonresponsive, or there are other environmental factors necessary for an immunogenic response to TSST-1. The percentage of Tokyo subjects who carry S. aureus and the percentage carrying TSST-1 strains are comparable to those in other countries (Seymour, unpublished report). Although a woman's exposure to S. aureus can vary over time (37), it can be reasonably assumed that Japanese women also have exposure over time. Thus, exposure to TSST-1 strains should occur at a frequency similar to that in other countries. The U.S. study assessed the genetic capabilities of Japanese women to respond to TSST-1. Inclusion criteria for the U.S. study required that Japanese women who participated in this study be of Japanese descent in order to control for potential marked genetic differences such as HLA haplotype. The fact that Japanese women living in the United States had a higher rate of seropositivity than those living in Tokyo suggests that the Tokyo Japanese women have the immunological capability to achieve the same anti-TSST-1 antibody titers as their U.S. Japanese cohorts. Therefore, the difference between the seropositivities of the Tokyo Japanese women and the U.S. Japanese women suggests a strong environmental influence on the development of neutralizing antibodies.
This study was not powered to expose specific health and hygiene practices that might be critical determinants of seropositivity, but there is a suggestion, in this and a previous study (39), that sexual intercourse (and most likely other forms of intimate activity) predisposes women to antibody development, presumably by increasing exposure to new strains of the bacteria or by increasing the frequency of exposure to TSST-1-producing S. aureus strains. Other unidentified environmental factors may also be important. Women who lack antibody and become colonized with TSST-1-producing S. aureus are at risk of developing TSS, but this and previous studies (21, 39) have shown that, at any given time, most colonized women are already immune to TSST-1. Although the USA100 NTED type of S. aureus strain is apparently widespread in Japan, an unexpected finding of this study was the similarity between the predominant TSST-1-producing S. aureus strain colonizing Japanese study subjects and the S. aureus strain commonly associated with mTSS in the United States.
This study was funded by The Procter & Gamble Company, Cincinnati, OH.
J. Parsonnet and R. V. Goering received research support from the study sponsor.
Published ahead of print on 11 June 2008. ![]()
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