Is There Really a Heterosexual AIDS Epidemic in the United States? Findings from a Multisite Validation Study,

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1 American Journal of Epidemiology Copyright 1999 by The Johns Hopkins University School of Hygiene and Public Health All rights reserved Vol. 149, 1 Printed in U.S.A. Is There Really a Heterosexual AIDS Epidemic in the United States? Findings from a Multisite Validation Study, R. Monina Klevens, 1 Patricia L. Fleming, 2 Joyce J. Neal, Jianmin Li, 4 and the Mode of Transmission Validation Study Group The objective of this study was to verify the mode of exposure to the human immunodeficiency virus (HIV) among cases who obtained acquired immunodeficiency syndrome (AIDS) through heterosexual contact and to determine the proportion of cases initially reported with no risk but whose exposure may have been heterosexual. Adults aged >1 years with AIDS, diagnosed from 1992 through 1995 with heterosexual risk or no risk at six US study sites (Alabama, California, Florida, New Jersey, New York City, and Texas), were eligible. Heterosexual risk was validated in 82 (1,610/1,952) of the heterosexual cases. Men were more likely than women to have a risk other than heterosexual (24 vs. 1, 2 P < 0.01). An HIV risk was identified for 51 (55) of those cases with no risk, and men were more likely than women to remain without risk (48 vs. 8, X 2 P = 0.02). Of the 415 men with no risk, 215 (52) were reclassified: 94 (44) were men who had sex with men, 61 (28) were injection drug users, 48 (22) had a heterosexual risk, and 12 (6) had other exposures. Of the 219 women with no risk, 16 (62) were reclassified: 82 (60) had a heterosexual risk, 47 (5) were injection drug users, and 6 (4) had infection associated with transfusion. In conclusion, most cases reported with heterosexually acquired AIDS had valid heterosexual risk exposures. Am J Epidemiol 1999; 149: acquired immunodeficiency syndrome; heterosexuality; HIV; reproducibility of results In response to reports of rare opportunistic illnesses in previously healthy young men in Los Angeles, California, and in New York City, surveillance for what is now known as the human immunodeficiency virus (HIV) was initiated. Surveillance was essential in determining how this new agent was transmitted from person to person (1). Since the early years of the HIV epidemic, patterns of HIV transmission in the US population have changed, and reports of an emerging heterosexual epidemic have warranted concern and action by the public health community (2-4) and by the public (5). However, some in the lay press initially believed that the alerts of an emerging heterosexual HIV epidemic were disproportionate to the risk of Received for publication October 2, 1997, and accepted for publication May 11, Abbreviations: AIDS, acquired immunodeficiency syndrome; CDC, Centers for Disease Control and Prevention; HIV, human immunodeficiency virus. 1 Assessment Branch, Data Management Division, National Immunization Program, Centers for Disease Control and Prevention, Atlanta, GA. 2 Surveillance Branch, Division of HIV/AIDS Prevention, National Center for HIV, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA. Council of State and Territorial Epidemiologists, Atlanta, GA. 4 TRW, Atlanta, GA. Reprint requests to Marie Morgan, Centers for Disease Control and Prevention, 1600 Clifton Road, MS E-49, Atlanta, GA acquiring HIV through heterosexual contact, especially secondary heterosexual contact (i.e., contact with an infected heterosexual who has no other high-risk behaviors) (6, 7). Descriptions from surveillance data of the patterns of HIV transmission are also used to characterize populations at risk (8), target prevention and control programs (9), distribute resources for HIV-related services (10), and evaluate the effectiveness of interventions (11, 12). Because of the importance of surveillance data, periodic evaluation of the accuracy of the information collected is warranted. In Florida, a reported increase in the number of acquired immunodeficiency syndrome (AIDS) cases transmitted by heterosexual contact prompted an evaluation of the validity of these reports (1). After review, of those cases initially reported as having a heterosexual risk, documentation of previously unreported risks was available for 0 percent of them, which resulted in reclassification. For several reasons, cases not acquired heterosexually may be categorized as such in surveillance reports. Attributing HIV infection to heterosexual exposure may reflect the reluctance of some persons to report other behaviors such as male-to-male sex or injection drug use (14). As public health resources for conducting surveillance become scarcer, HIV risk may be incompletely ascertained by state and local health departments. Patients may deny or not know the risk

2 76 Klevens et al. behaviors of their partners, or providers may not ask about risk behaviors of patients or their partners. Some cases initially reported as having no risk were acquired heterosexually. No-risk cases are investigated by local health departments by using a standard protocol that includes a review of medical records, an interview with health care providers, and, as needed, a patient or proxy interview for priority cases (15). Through December 1996, 75,147 (1 percent) of the 57,800 AIDS cases among adults and adolescents were initially reported as no risk. Of these, 4,609 (46 percent) have been reclassified to known risk categories (16). A total of 67 percent of these cases in women and 1 percent in men were acquired heterosexually. This paper describes findings from medical records that were reviewed as part of a multisite validation study. The study was conducted by the Centers for Disease Control and Prevention (CDC) to measure the accuracy of risk classification of cases reported with heterosexually acquired AIDS; to quantify the likelihood of risk reclassification by sex, age, race, and reporting source; and to measure the proportion of cases that are reported as no risk but may be acquired heterosexually. MATERIALS AND METHODS All 50 US states, the District of Columbia, and US dependencies and possessions report AIDS cases to CDC by using a uniform surveillance case definition (16). Most case reports are initiated by providers or health department surveillance personnel at health care facilities after they abstract information from patient medical charts. Risk information from medical records is collected by using standard definitions for each route of HIV transmission. In addition, state and city surveillance programs use other methods to report AIDS cases, such as matching reports to tuberculosis and tumor registries and reviewing death certificates. To describe national trends in AIDS among cases with a heterosexual risk or no risk, we plotted the estimated number of adults and adolescents (aged >1 years) reported with AIDS by year of diagnosis from 1984 through 1994 and reported to CDC through December 1, Because of delays between the date of AIDS diagnosis and the date of report, probabilities of a case being reported within a certain time period are used to adjust trends for reporting delays (17). These probabilities are calculated by using the previous 6 years of AIDS case reports. In addition, an adjustment is used to estimate when an AIDSopportunistic illness will develop in cases reported with the CD4+ criterion added to the 199 AIDS surveillance case definition (17). This latter adjustment is estimated on the basis of data from a large longitudinal study of the spectrum of HIV disease (18). Six sites participated in the study: Alabama, California (excluding San Francisco and Los Angeles Counties), four Florida counties (Broward, Dade, Palm Beach, and St. Lucie), New Jersey, New York City, and Texas (excluding Houston and Brazoria Counties). Study sites were not selected to be representative of the United States; rather, selection was based on an objective review of applications for AIDS surveillance funds earmarked for this study. At each of the six study sites, the following types of medical records were reviewed to identify the route by which each case may have become HIV infected: hospital inpatient charts, outpatient clinic charts, records from sexually transmitted disease clinics, health department registries of other diseases such as tuberculosis and hepatitis, and social services records. At three sites HIV counseling and testing records were also reviewed, at two sites information was obtained from interviews in an independent study, and at one site partner notification records were also reviewed. Sample sizes were calculated by using the arcsin square root transformation, assuming a site-specific misclassification of heterosexual cases (10-25 percent) with a binomial distribution (19). After drawing an initial sample, we revised the sample size on the basis of preliminary analyses of the first sample. Samples consisted of men and women (aged >1 years) who were reported as having AIDS, and either a heterosexual risk or no risk, selected within each stratum by random number generation. Those AIDS cases eligible for sample 1 were diagnosed in 1992 and were reported through September 199; however, because record reviews were conducted in 1994, as many as 50 percent of those cases had died and thus could not be interviewed. Interviews were desired for another component of this study. Therefore, for the remaining samples, cases reported within 6 months of diagnosis were selected as follows: sample 2, cases diagnosed from August 1, 1994, through December 0, 1994, and reported through February 28, 1995; sample, cases diagnosed from November 1, 1994, through March 0, 1995, and reported through May 0, 1995; and sample 4, cases diagnosed from February 1, 1995, through June 0, 1995, and reported through August 0, In a few instances, a case was sampled twice; however, only one investigation was conducted. To account for differences in the probabilities of selection, sampling fractions were monitored by stratum (i.e., sex and risk) and factored into the standard errors for x 2 testing and logistic modeling by using SUDAAN statistical software, version 6.4 (Research Triangle Institute, Research Triangle Park, North Carolina) (20). Am J Epidemiol Vol. 149, 1, 1999

3 US Heterosexual AIDS Epidemic 77 We considered a heterosexual-contact case validated if investigators found documentation of heterosexual risk in at least one record in addition to the record from which the case report was submitted. When heterosexual risk is documented, information on the HIV status and risk behavior of the partner (e.g., injection drug use, bisexual activity) is collected. When heterosexual contact with an HIV-positive person is documented, but that person's risk behavior is not specified, the case is still considered heterosexual. We defined reclassification as a change in risk from that initially reported (either heterosexual or no risk) to one higher in the hierarchy after follow-up. The hierarchy is used in surveillance to present information on persons reported with more than one risk (16): men who have sex with men, injection drug users, men who have sex with men and are injection drug users, recipients of clotting factor for hemophilia or other coagulation disorders, those who have heterosexual relations with an HIV-infected person or who have one of the risks already listed, or recipients of HIVinfected blood or blood components other than clotting factor or of HIV-infected tissue. Analyses of heterosexual risk cases were conducted separately from those of no-risk cases. In addition, cases with heterosexual risk initially classified as having sex with an HIV-infected partner whose risk was unspecified were analyzed as part of the heterosexual risk group and independently. The term reclassified was also used to describe heterosexual-contact cases reported with an unspecified partner risk if, after investigation, the partner's risk was identified. Excluded were those cases in the sample that could not be followed up because records were not available; we also excluded cases with no risk information (A 1 CO in 4 O. in in CO «2 I 1 available from the medical records. We assessed differences in the characteristics of cases included and excluded from further analyses by using the 2 test for independence (19). To assess characteristics (e.g., age or sex) that might be associated with the case versus correlates of surveillance methods (e.g., source of report), we used logistic modeling to calculate the likelihood of reclassification (20). Separate models were calculated by sex and for each characteristic of the case or of surveillance. For each stratum, the category with the lowest frequency of reclassification was used as the referent. Data on strata with fewer than 10 observations are not presented. RESULTS Nationally, through 1994, the number of AIDSopportunistic illnesses increased in cases reported as having heterosexual risk and no risk (figure 1). The number of heterosexual cases among women was substantially higher than that among men. In addition, the number of cases reported with no risk, especially men, increased rapidly from 1992 to At the six study sites, 8,67 adults met the sex and risk criteria; of these, we sampled and enrolled,649 AIDS cases. For 78 (10.4 percent) of these adults, risk was reclassified by surveillance staff as part of routine case finding procedures, after sampling but before field assignment. Of the remaining,271 adults, 72.7 percent (2,78) were initially reported as having a heterosexual risk, and 89 (27. percent) were reported as having no risk. For 45 of the cases with a heterosexual risk and 165 with no risk, records were not available because of out-of-state residence or Men yrith noriskreported ion x.. "". «*"*"* He>SVosexual men ^ ^ WWomeriwith no"riskreported Year of diagnosis FIGURE 1. Estimated incidence of AIDS-opportunistic illness, adjusted for reporting delays and the 199 change in the surveillance case definition, among adults reported as having heterosexual risk or no risk, by sex, United States, Am J Epidemiol Vol. 149, 1, 1999

4 78 Klevens et al. because the facility that reported the case had no records. For an additional 82 cases with a heterosexual risk and 94 cases with no risk, records were reviewed but no HIV-related risk information was found. Aggregate characteristics of the cases with followup and with risk information were compared with those with no follow-up or with no risk information (table 1). Cases with and without follow-up were similar in age. However, those not followed up were more likely to have no risk, be male, be white non-hispanic, be sampled in California or Texas, and be reported from laboratories. Of those adults initially reported as having heterosexually acquired AIDS, 76 percent of the men and 87 percent of the women had valid reports of heterosexual risk (table 2). Of the men initially reported with no risk, 52 percent were reclassified; of those reclassified, 22 percent had a heterosexual risk (table 2). Of those women initially reported with no risk, 62 percent were reclassified; of these, 60 percent had a heterosexual risk. Most of the cases who had heterosexual contact with an HIV-infected partner whose risk was unspecified (49 percent of the cumulative heterosexualcontact cases) (16) remained in this category after investigation (66 percent of the men and 69 percent of the women). Of the 4 percent of men and 1 percent of women who were initially reported in this category and were then reclassified, approximately 4 percent of both men and women were injection drug users (figure 2). Among the reclassified women, an additional 4 percent were the heterosexual contacts of injection drug users. TABLE 1. Characteristics of AIDS* cases, by inclusion or exclusion} from analyses, Mode of Transmission Validation Study, Initial risk Heterosexual No risk Sex Male Female Characteristic Age group (years) < >50 Race}: White Black Hispanic Asian/Pacific Islander American Indian/Alaskan native Study site Alabama California Florida New Jersey New York City Texas Source of report (records)}: Private physician Prison Inpatient Databases Laboratory Outpatient 1, ,214 1, , , Included (n = 2,586) Excluded (n = 685) P value <0.01 <0.01 >0.05 <0.05 <0.01 <0.01 * AIDS, acquired immunodeficiency syndrome. t Cases excluded were those with no available records. Data on cases with no responses regarding race and/or source of report have not been included in this table. Am J Epidemiol Vol. 149, 1, 1999

5 US Heterosexual AIDS Epidemic 79 TABLE 2. Reclassification of risk among AIDS* cases initially reported with heterosexual risk or no risk, by sex, Mode of Transmission Validation Study, risk MSM* Injection drug use MSM + injection drug use Hemophilia Heterosexual Sex with HIV* positive Sex with specified high risk Transfusion No risk/other Men (n = 799) Heterosexual risk <1 76 <1 Women (n= 1,15) , <1 Men (n = 415) No risk Women (n = 219) * AIDS, acquired immunodeficiency syndrome; HIV, human immunodeficiency virus; MSM, men who have sex with men. Men Men who have sex with men 4 Women Sex with drug user, 4 Transfusion recipien 2 lemophilia, Injection drug users 42 Heterosexual, 15 ^ * M e n who have sex with men and inject drugs, 6 Sex with transfusion recipient, 1 Sex with bisexual male 12 Injection drug users, 4 Transfusion recipient, Total (n = 2,586) , <1 <1 67 <1 11 FIGURE 2. Risk categories for those adult men and women initially reported as having heterosexual contact with an HlV-infected partner whose risk was unspecified who could be reclassified after follow-up, Mode of Transmission Validation Study, The odds of reclassification of cases initially reported with heterosexual risk are listed in tables and 4; the latter table presents information on cases initially reported as being contacts of HlV-infected heterosexual partners whose risk was unspecified. The frequency of reclassification was lower among older AIDS cases. Among women, the odds of reclassification were higher for blacks; Hispanic women initially reported as being heterosexual were also more likely than white non-hispanic women to be reclassified. Among heterosexual men whose partner's risk was unspecified, blacks were slightly more likely than Hispanics to be Am J Epidemiol Vol. 149, 1, 1999

6 80 Klevens et al. TABLE. Likelihood of reclassification* among AIDSt cases initially reported with heterosexual risk., by sex, Mode of Transmission Validation Study, Age (years) < >50 Race White Black Hispanic Asian/Pacific Islander American Indian/ Alaskan native Study site Alabama California Florida New Jersey New York City Texas Source of report (records) Private physician Prison Inpatient Databases Laboratory Outpatient reclassified Men (n = 799) ratio reclassified Women (n= 1,15) ratio * Includes cases reclassified to male-male sex; injection drug use; recipients of clotting factor for hemophilia or other clotting disorder; and recipients of human immunodeficiency virus (HIV) positive blood, components, or tissue, t AIDS, acquired immunodeficiency syndrome. reclassified. There were significant differences in the odds of reclassification by participating study site, especially among men. Men with AIDS reported from databases and outpatient records and women with AIDS reported from alternate databases (e.g., disease and medication registries, insurance and study databases) had the lowest frequency of reclassification. Among cases initially reported with no risk, significant differences in the odds of risk reclassification were observed among men (table 5). The correlates of reclassification included younger age, being white or Asian/Pacific Islander, participating study site, and outpatient or laboratory reporting source. For women, only a laboratory reporting source and two participating study sites (New Jersey and Texas) were significant correlates of reclassification (table 5). DISCUSSION From the review of medical records, we found that 82 percent of the cases initially reported as acquired heterosexually were valid and that AIDS in one fifth of the men and more than half of the women initially reported as having no risk was probably acquired heterosexually. These findings support the reports of an emerging heterosexual AIDS epidemic in the United States. The number and proportion of adults, especially women, who have been reported with AIDS attributed to heterosexual contact have increased (4). HIV seroprevalence studies suggest increases in HIV infection among women (21). We also observed increases in the numbers of cases reported with no risk; a proportion of them are heterosexual. Heterosexuals at highest risk should be characterized so that prevention programs can be implemented accordingly (). These findings confirm the reality of a heterosexual epidemic of HIV infection in the United States; however, not all heterosexuals are at equal risk of becoming infected. Of those cases of heterosexually acquired AIDS reported in 1996, 7 percent had heterosexual contact with an injection drug user, a hemophiliac, a transfusion recipient, or a bisexual male (i.e., primary Am J Epidemiol Vol. 149, 1, 1999

7 US Heterosexual AIDS Epidemic 81 TABLE 4. Likelihood of reclassification* among AIDSf cases initially reported with heterosexual contact with a partner whose risk is unspecified, by sex, Mode of Transmission Validation Study, Men (n = 478) redassifiec1 ratio 95 reclassified Women (n = 627) ratio 95 Age (years) >50 Race White Black Hispanic Asian/Pacific Islander American Indian/ Alaskan native Study site Alabama California Florida New Jersey New York City Texas Source of report (records) Private physician Prison Inpatient Databases Laboratory Outpatient * Includes cases reclassified to male-male sex; injection drug use; recipients of clotting factor for hemophilia or other clotting disorder; and recipients of human immunodeficiency virus (HIV) positive blood, components, or tissue, t AIDS, acquired immunodeficiency syndrome. heterosexual transmission). This proportion was higher among women (45 percent), especially white women (65 percent), and lowest among men (28 percent), especially black (27 percent) and Hispanic (28 percent) men (16). In our study, two thirds of those cases reported with heterosexually acquired AIDS remained in a category in which heterosexual transmission from a partner in a primary risk group could not be validated; therefore, secondary transmission probably accounts for a proportion of heterosexual AIDS cases. Additional information on the risk behaviors of the heterosexual partners of those in this group will be available from interviews conducted as another component of this study. Persons who engage in high-risk heterosexual contact should be aware of the potential for secondary heterosexual transmission from partners who have no primary risk behaviors. Because study sites were not selected at random, findings may not be generalizable to national AIDS surveillance. To assess whether findings from this study represent cases reported nationally to AIDS surveillance, we compared the characteristics of AIDS cases reported from participating study sites with all cases reported in the United States from 1994 through Hispanics with AIDS were slightly overrepresented at our study sites (2 percent) compared with those in the United States (19 percent); the difference between the frequencies of all other variables was less than or equal to 2 percent. Many Hispanics with AIDS are reported from California, New York City, Florida, and Texas (all sites that participated in this study). Although participating study sites were not selected at random, the similarity between cases from these sites and cases reported nationally suggests that findings from this study are generalizable. Applying these results to the United States would mean that, for example, the number of heterosexually acquired AIDS cases reported in 1995 is slightly conservative (1 percent in men and percent in women) (22). Our findings are consistent with those from a similar study conducted in Florida, in which a review of medical charts and records from sexually transmitted Am J Epidemiol Vol. 149, 1, 1999

8 82 Klevens et al. TABLE 5. Likelihood of reclassification* among AIDSt cases initially reported with no risk, by sex, Mode of Transmission Validation Study, reclassified Men (n = 415) ratio 95 reclassified Women (n = 219) ratio 95 Age (years) >50 Race White Black Hispanic Asian/Pacific Islander American Indian/ Alaskan native Study site Alabama California Florida New Jersey New York City Texas Source of report (records) Private physician Prison Inpatient Databases Laboratory Outpatient * Includes cases reclassified to male-male sex; injection drug use; recipients of clotting factor for hemophilia or other clotting disorder; and recipients of human immunodeficiency virus (HIV) positive blood, components, or tissue, t AIDS, acquired immunodeficiency syndrome. disease clinics resulted in reclassification of 29 percent of the men and 10 percent of the women initially reported as heterosexual (1). Men may be more frequently misclassified as heterosexual because of the stigma related to acknowledging homosexual activity (14). Men and women may deny injection drug use for many reasons, including social desirability and fear of repercussions (2). Our reclassification of men (52 percent) and women (62 percent) with no risk is consistent with the reclassification of ADDS in cases reported to national surveillance as having no risk (8 percent) and were diagnosed when the cases in our study were diagnosed ( ) (CDC, unpublished data, 1997). Of those cases initially reported with no risk but for whom risk was found in this study, a higher proportion of men (22 vs. 15 percent) and a lower proportion of women (61 vs. 67 percent) were reclassified to the heterosexual exposure category compared with all those diagnosed with AIDS during a similar period (CDC, unpublished data, 1997). We expected to reclassify fewer cases in this study compared with national surveillance; as routine surveillance activities continued, those cases that were the most difficult to reclassify were left in the no-risk category and would have been sampled in this study. However, we reclassified a higher proportion of men, perhaps because men reported with no risk are currently not a priority for follow-up in national surveillance. After we reviewed the records, a group for whom no risk information was available remained: perhaps the patient did not report risk to the health care provider, the patient did not know or perceive that he or she was at risk, or the health care provider did not ask about or record risk. This issue will be evaluated further when patients and health care providers are interviewed as part of this study. Most cases initially reported with no risk are reclassified after investigation (16). Still, if risk were better documented, most of these investigations would be unnecessary. There are many reasons for poor documentation of HIV risk in patient records: a patient's denial of risk (2), a patient's lack of awareness of his or her risk (e.g., unaware that the Am J Epidemiol Vol. 149, 1, 1999

9 US Heterosexual AIDS Epidemic 8 Am J Epidemiol Vol. 149, 1, 1999 partner has a primary risk), fear of discrimination or of losing insurance (24), physicians not conducting risk assessment because they think that patients will be offended by questions about sexual behaviors (25), lack of physician training in taking drug and sexual histories (26), or physician assumptions that their patients are not at high risk (27). Physicians and ancillary staff are encouraged to understand their larger role in the prevention of HTV and to improve the collection and recording of risk information (2, 26). Only by improving risk ascertainment and documentation of risk in medical records can surveillance monitor HIV transmission patterns efficiently and accurately. Our analysis indicated that reports of heterosexual transmission among cases aged 50 years or older were more valid than those among younger cases. This finding could be due to confounding, because higher proportions of younger cases in this study were reported from outpatient sites, laboratories, and alternate databases, which in turn were more likely to yield valid risk. It is possible that because of the frequency of transfusions among older persons, they may unknowingly infect a partner heterosexually. Also, older persons with AIDS may be more likely to discuss with their health care providers how they became infected. Reclassification varied widely by study site, suggesting that factors inherent in local surveillance methods are associated with validity of risk. Surveillance practices are difficult to standardize completely because states have different reporting laws, disease burdens, and resources. However, all surveillance programs could routinely assess risk validity on a representative sample of those HIV/AIDS cases reported; as of fiscal year 1997, funding for US AIDS surveillance requires such evaluations. Limitations of this study include a bias in follow-up by race; thus, we may have overestimated the likelihood of misclassification of black and Hispanic women compared with white women. Because higher proportions of Hispanic women (4 percent) are reported with heterosexually acquired AIDS compared with white (7 percent) and black (4 percent) women (16), differences in the proportions of heterosexually acquired AIDS may have been overestimated. In addition, from this study we cannot infer misclassification of heterosexual cases reported before However, because fewer of the earlier cases had a heterosexual risk, the effect of misclassification is almost negligible. Knowledge of the HIV exposure mode is essential to enable the planning and targeting of effective HIV prevention interventions. Health care workers and public health personnel should make every effort to identify and record accurate risk information among persons with HIV/AIDS. Periodic validation of risk information, including patient interviews, will further ensure the accuracy of risk information in AIDS surveillance. ACKNOWLEDGMENTS The Mode of Transmission Validation Study Group includes the following people and study sites: Richard Holmes, Alabama Department of Health, Montgomery, Alabama; James N. Creeger, California Department of Health, Sacramento, California; Lisa Conti, Penny Crews, Michael Greene, and Queen Holden, Florida Department of Health, Tallahassee, Florida; Samuel Costa and John Beil, New Jersey Department of Health, Trenton, New Jersey; Pauline A. Thomas, Amelia Chu, and Alfreda Torbett, New York City Department of Health, New York, New York; and Richard Armor and Douglas Hamaker, Texas Department of Health, Houston, Texas. The authors thank Dr. John Karon and Tim J. Bush for their suggestions and their assistance with sampling and Dr. Robert Frey for his assistance with the analysis. 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