Age-adjusted Seroprevalence Research Articles

Occult hepatitis B in the genotype H‐infected Nahuas and Huichol native Mexican population

Mexico is considered to be a low endemic country for HBV infection. However, a high anti-HBc against a low hepatitis B surface antigen (HBsAg) seroprevalence is the reported characteristic of native Mexicans. HBV diagnosis and genotype distribution was examined in native populations (Nahuas and Huichol, n = 306), and compared to a non-native population (Mestizos, n = 17). Overall, 6% of the natives were positive for HBsAg and 33% had detectable anti-HBc. HBsAg prevalence was lower in Nahuas compared to Huichols (1.4% vs. 9.4%, P < 0.002). Occult hepatitis B was detected in 14.2% (41/289) of natives, who either tested positive (5.88%, 17/289 HBsAg-negative) or negative for anti-HBc marker (8%, 24/289 HBsAg-negative). Age-adjusted anti-HBc seroprevalence and HBsAg quantitation revealed a sub-optimal sensitivity of conventional immunoassays. Nahuas had HBV/H and Huichol had HBV/A as the predominant genotypes followed by genotypes D, C, B, A, and D, G and H, respectively. A less variable HBV/H was characteristic in Mestizos, compared to a much variable HBV/H identified among the Nahuas. In conclusion, these findings indicate a high HBV endemicity among native Mexican groups where occult B infection is common. The different distribution of HBV genotypes among natives suggests multiple reservoirs of HBV from which these genotypes spread into the local communities. High anti-HBc seroprevalence against a low HBsAg prevalence rate may be due to the limited sensitivity of the immunoassays for the detection of HBsAg that are available in Mexico and/or unknown immunogenetic characteristics of native Mexicans.

Cytomegalovirus seroprevalence in the United States: the national health and nutrition examination surveys, 1988-2004.

BACKGROUND. Congenital cytomegalovirus (CMV) infection causes permanent disabilities in more than 5500 children each year in the United States. The likelihood of congenital infection and disability is highest for infants whose mothers were CMV seronegative before conception and who acquire infection during pregnancy. METHODS. To provide a current, nationally representative estimate of the seroprevalence of CMV in the United States and to investigate trends in CMV infection, serum samples from the National Health and Nutrition Examination Survey (NHANES) 1999-2004 were tested for CMV-specific immunoglobulin G antibody, and results were compared with those from NHANES III (1988-1994). Individuals aged 6-49 years (21,639 for NHANES III and 15,310 for NHANES 1999-2004) were included. RESULTS. For NHANES 1999-2004, the overall age-adjusted CMV seroprevalence was 50.4%. CMV seroprevalence was higher among non-Hispanic black and Mexican American children compared with non-Hispanic white children and increased more quickly in subsequent age groups. CMV seropositivity was independently associated with older age, female sex, foreign birthplace, low household income, high household crowding, and low household education. Compared with NHANES 1988-1994, the overall age-adjusted CMV seroprevalence for NHANES 1999-2004 was not significantly different. CONCLUSIONS. Many women of reproductive age in the United States are still at risk of primary CMV infection during pregnancy. There is an urgent need for vaccine development and other interventions to prevent and treat congenital CMV. The substantial disparities in CMV risk among seronegative women suggest that prevention strategies should include an emphasis on reaching racial or ethnic minorities and women of low socioeconomic status.

Declining Hepatitis A Antibody Seroprevalence in the Korean Military Personnel

We retrospectively analyzed serological test results for anti-hepatitis A virus immunoglobulin G (anti-HAV IgG) of sera collected from 779 military personnel during January 2001 to May 2008. The overall seroprevalence of anti-HAV IgG of the subjects was 17.5% (95% confidence interval [CI], 14.8-20.1%). When adjusted to the age-specific distribution of the army population, the age-adjusted seroprevalence was 14.6% (95% CI, 13.0-16.3%). All subjects who were 40 years and over had anti-HAV IgG. Meanwhile, the seroprevalence of anti-HAV IgG for those 24 years and younger was 4.7%. This low prevalence rate among young military personnel calls for stricter adherence to vaccination policies and stronger requirements for military HAV vaccination programs.

Hand, foot and mouth disease: seroprevalence of Coxsackie A16 and Enterovirus 71 in Germany

Coxsackie A16 (CA16) and Enterovirus 71 (EV71) are members of the picornaviridae family and are associated with hand, foot and mouth disease (HFMD), in rare cases also to acute neurological diseases. HFMD outbreaks have been reported from many parts of the world, especially Southeast Asia. The objective of the study was to analyze CA16 and EV71 seroepidemiologically in the population of Frankfurt/M., Germany. A total of 696 individuals (349 males and 347 females, divided into seven different age groups, 1-4, 5-9, 10-14, 15-19, 20-39, 40-59 and >60 years) were tested for serum antibodies against CA16 and EV71 by the use of a microneutralization test. Sera were collected at the Frankfurt university hospital from patients suffering from other diseases between March and September 2006. CA16 and EV71 infections were observed to be widely present in the population. The age-adjusted seroprevalence for individuals >or=1 year was found to be 62.9% for CA16 and 42.8% for EV71 without a gender-specific significant difference. Only 12.0 and 27.0% of the children aged 1-4 had antibodies to EV71 and CA16, respectively - indicating that 88 and 73% of the children in this age group were susceptible to the infection. A total of 213 individuals (30.6%) was seropositive for both viruses, 303 (43.5%) showed neutralizing antibodies (NtAb) to at least one of the two viruses. A total of 180 individuals (25.9%) revealed no antibodies. High CA16 and EV71 antibody titers were found especially in the age group of the 10- to 14-year-olds, without gender-specific difference. The seroprevalence study demonstrates a common spread of CA16 and EV71 in Germany, but a relatively high susceptibility of the younger population to CA16 and EV71. Obviously, the manifestation rate, i.e., distinct disease of these infections is low.

Herpes simplex virus seroprevalence among children, adolescents and adults in Greece

The aim was to study the type-specific seroprevalence of Herpes simplex virus (HSV)-1 and HSV-2 infections and the associated risk factors in children, adolescents and adults in Greece. A total of 1867 serum samples from children, adolescents and adults of both genders aged from 0 to 60 years were collected from three large hospital-referral centres in Athens. All sera were tested for type-specific antibodies to HSV-1 and HSV-2 using HerpeSelect IgG ELISA tests (Focus Diagnostics Cypress, Cal, USA). Overall age-adjusted seroprevalence of HSV-1 and HSV-2 was 72.0% and 10.2%, respectively. HSV-1 seropositivity was low in children up to nine years of age, increased sharply in adolescence, and was higher in females than males in each group surveyed. HSV-2 seropositivity was low (0.8%) below 20 years of age and increased to a maximum prevalence of 18.7% in men and 22.7% in women. Multivariate risk factor analyses indicated that HSV-1 seropositivity was associated with socioeconomic indicators (e.g. lower educational level, residency outside greater Athens), whereas HSV-2 was associated with sexual behavioural factors (e.g. being divorced, greater number of lifetime sexual partners). HSV-2 risk factor profiles were similar in women and in men. This first large seroprevalence study in Greece showed a high age-standardized HSV-1 seropositivity after adolescence and a relatively low age-standardized HSV-2 seroprevalence from birth to 60 years of age. Dual seropositivity to HSV-1 and HSV-2 was low (0.6%) in females under 20 years of age, suggesting that the potential use of an HSV-2 prophylactic vaccine in adolescents could reduce the spread of HSV-2 infection.

Hepatitis A incidence and hospital-based seroprevalence in Italy: a nation-wide study

To define the pattern of HAV infection in Italy and to study the differences among geographic areas (northern, central and southern Italy) and age-classes, we performed HAV antibody testing on sera collected in 1996-1997 from a large sample of the Italian population and compared the results with those of other seroprevalence studies and with incidence data for the period 1985-2005, calculated by a surveillance system specific for acute viral hepatitis based on symptomatic cases. A total of 3,561 sera, collected by hospital-based reference laboratories in 18 out of 20 Italian Regions, were tested; 1,138 (32%, 95% CI: 30.5-33.5) were positive. The age-adjusted prevalence was 60.1% and the age-specific rates were among the highest rates reported in Europe in the 1990s. The age-adjusted seroprevalence showed a significant north-south gradient, increasing from 55% in northern Italy to 68% in southern Italy. Age and area of residence were found to be strong predictors of previous HAV infection: the marked increase in prevalence with increasing age represents a strong cohort effect. In northern Italy, a marked increase with age was observed beginning with the 20- to 29-year age-class, whereas in southern Italy, such an increase was observed beginning with the 12- to 19-year age-class, indicating that northern Italy preceded southern Italy by 10-20 years in terms of improvements in hygiene and sanitation. The incidence of HAV infection shows an evident peak in 1997, when an outbreak occurred in southern Italy, mainly affecting 15- to 24-year-old individuals. In the period from 1998 to 2005, the incidence drastically decreased (average of 3.2/100,000 inhabitants), reaching a minimum of 2/100,000 inhabitants in 2005.

EVALUATION OF TWO TOXOPLASMA GONDII SEROLOGIC TESTS USED IN A SEROSURVEY OF DOMESTIC CATS IN CALIFORNIA

We evaluated the sensitivity (Se) and specificity (Sp) of an IgG enzyme-linked immunosorbent assay (ELISA) and IgG indirect fluorescent antibody test (IFAT) for detection of Toxoplasma gondii-specific antibodies in sera from 2 cat populations using a Bayesian approach. Accounting for test covariance, the Se and Sp of the IgG ELISA were estimated to be 92.6% and 96.5%, and those of the IgG IFAT were 81.0% and 93.8%, respectively. Both tests performed poorly in cats experimentally coinfected with feline immunodeficiency virus and T. gondii. Excluding this group, Se and Sp of the ELISA were virtually unchanged (92.3% and 96.4%, respectively), whereas the IFAT Se improved to 94.2% and Sp remained stable at 93.7%. These tests and an IgM ELISA were applied to 123 cat sera from the Morro Bay area, California, where high morbidity and mortality attributable to toxoplasmosis have been detected in southern sea otters. Age-adjusted IgG seroprevalence in this population was estimated to be 29.6%, and it did not differ between owned and unowned cats. Accounting for Se, Sp, and test covariances, age-adjusted seroprevalence was 45.0%. The odds for T. gondii seropositivity were 12.3-fold higher for cats aged >12 mo compared with cats aged <6 mo.

Trends in Herpes Simplex Virus Type 1 and Type 2 Seroprevalence in the United States

Herpes simplex virus type 1 (HSV-1) and type 2 are common infections worldwide. Herpes simplex virus type 2 (HSV-2) is the cause of most genital herpes and is almost always sexually transmitted. In contrast, HSV-1 is usually transmitted during childhood via nonsexual contacts. Preexisting HSV-1 antibodies can alleviate clinical manifestations of subsequently acquired HSV-2. Furthermore, HSV-1 has become an important cause of genital herpes in some developed countries. To examine trends in HSV-1 and HSV-2 seroprevalence in the United States in 1999-2004 compared with 1988-1994. Cross-sectional, nationally representative surveys (US National Health and Nutrition Examination Surveys [NHANES]), were used to compare national seroprevalence estimates from 1999-2004 with those from 1988-1994, and changes in HSV-1 and HSV-2 seroprevalence since 1976-1980 were reviewed. Persons aged 14 to 49 years were included in these analyses. Seroprevalence of HSV-1 and HSV-2 antibodies based on results from type-specific immunodot assays; diagnosis of genital herpes. The overall age-adjusted HSV-2 seroprevalence was 17.0% (95% confidence interval [CI], 15.8%-18.3%) in 1999-2004 and 21.0% (95% CI, 19.1%-23.1%) in 1988-1994, a relative decrease of 19.0% between the 2 surveys (95% CI, -28.6% to -9.5%; P<.001). Decreases in HSV-2 seroprevalence were especially concentrated in persons aged 14 to 19 years between 1988 and 2004. In adolescents aged 17 to 19 years and young adults, the decreases in HSV-2 seroprevalence were significant even after adjusting for changes in sexual behaviors. Among those infected with HSV-2, the percentage who reported having been diagnosed with genital herpes was statistically different (14.3% in 1999-2004 and 9.9% in 1988-1994; P = .02). Seroprevalence of HSV-1 decreased from 62.0% (95% CI, 59.6%-64.6%) in 1988-1994 to 57.7% (95% CI, 55.9%-59.5%) in 1999-2004, a relative decrease of 6.9% between the 2 surveys (95% CI, -11.6% to -2.3%; P = .006). Among persons infected with HSV-1 but not with HSV-2, a higher percentage reported having been diagnosed with genital herpes in 1999-2004 compared with 1988-1994 (1.8% vs 0.4%, respectively; P<.001). These data show declines in HSV-2 seroprevalence, suggesting that the trajectory of increasing HSV-2 seroprevalence in the United States has been reversed. Seroprevalence of HSV-1 decreased but the incidence of genital herpes caused by HSV-1 may be increasing.

Seroprevalence of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in former East and West Germany, 1997?1998

The aim of this study was to investigate the seroprevalence of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in representative samples of the total former East German (FEG) and total former West German (FWG) populations. Type-specific testing with the HSV-1 (gG1) and HSV-2 (gG2) indirect ELISA was performed on an age- and sex-stratified random subsample of 3,792 sera collected during the 1997-1998 German National Health Survey. Weighted seroprevalence estimates were calculated for the total FEG and FWG populations. The overall age-standardised seroprevalence of HSV-1 was 82.6% in Germany, 85.5% (95%CI, 83.4-87.3%) in FEG and 81.8% (95%CI, 79.9-83.6%) in FWG. The overall seroprevalence of HSV-2 was 13.3% (95%CI, 11.8-14.9) in Germany, 16.5% (95%CI, 14.1-18.9) in FEG and 12.6% (95%CI, 10.7-14.5%) in FWG. The difference between FEG and FWG was largely due to the significantly higher age-adjusted seroprevalence of HSV-1 and HSV-2 in women (but not men) in FEG as compared to FWG. The HSV seroprevalence estimates in this study are consistent with results of previous less representative seroprevalence studies in Germany. Differences in HSV-2 seroprevalence between FEG and FWG suggest differences in sexual behaviour that warrant further investigation.

Antibodies reactive to Rickettsia rickettsii among children living in the southeast and south central regions of the United States.

The reported annual incidence of Rocky Mountain spotted fever in the United States is 2.2 per million, but studies have suggested that human infection with Rickettsia rickettsii may be more common. This study estimated the prevalence of antibodies reactive to R rickettsii among children living in the southeastern and south central United States. Approximately 300 specimens were obtained from children at each of 7 pediatric referral centers (N = 1999). Serum was tested for R rickettsii antibodies by means of indirect immunofluorescence antibody assay. Three different cutoff titers (>or=64, >or=128, and >or=256) represented increasing levels of stringency to define positive specimens. Overall, 12.0% of children had R rickettsii antibody titers of at least 64; 7.3%, at least 128; and 4.3%, at least 256. Strong relationships were seen between increasing age and seroprevalence at each cutoff titer. Remarkably, 6.4% of children aged 13 to 17 years had titers of at least 256. Age-adjusted seroprevalence rates at titers of at least 64 varied from 21.9% in Little Rock, Ark, to 3.5% in Louisville, Ky. At titers of at least 256, seroprevalence ranged from 7.7% in Nashville, Tenn, to 1.8% in Winston-Salem, NC. Only site and age group were strong predictors of seropositivity; a weak association was seen with nonurban residence. To our knowledge, this is the largest serosurvey of rickettsial infection in children in the United States. Within the limitations of the immunofluorescence antibody assay, these data suggest that infections with R rickettsii or antigenically related spotted-fever group rickettsiae may be common and subclinical. The results also have implications for the interpretation of single immunofluorescence antibody assay titers in children with suspected Rocky Mountain spotted fever.

Endemic hepatitis C virus infection in a seaboard village of southwestern Taiwan.

This study investigated the rate of Hepatitis C Virus (HCV) infection and identified the risk factors associated with a HCV infection at Ma-Sha-Gou, a seaboard village in southwestern Taiwan. In total, 240 subjects were sampled and stratified according to age and sex from 1,200 residents aged 20-64 years old. HCV-specific antibodies (anti-HCV Ab) in blood specimens were tested for HCV seropositive by the third-generation HCV ELISA system. The subjects, later identified as 152 seropositive and 88 seronegative, were selected for analysis of the correlates of HCV infection. They were interviewed to explore a variety of possible risk factors for HCV infection with a structured questionnaire. The results showed that the anti-HCV age-adjusted seroprevalence was 55.8%. Needle injection was significant to the increased anti-HCV seroprevalence, with multivariate age-adjusted odds ratio (OR) and confidence interval (CI) of 1.9 and 1.2-3.9 respectively. This study identifies Ma-Sha-Gou as an endemic area of HCV infection, in which needle injection from any medical activity was a possible transmission pathway in the village, and suggests the health authorities/community health nurses should give the residents a comprehensive community-based education program to interrupt HCV transmission.

Ehrlichia chaffeensis seroprevalence among children in the southeast and south-central regions of the United States.

The reported annual incidence of human monocytic ehrlichiosis, which is due to infection with Ehrlichia chaffeensis, is as high as 5.5 per million in some states, but serosurveys suggest much higher infection rates in some populations. To estimate the prevalence of E chaffeensis infection among children aged 1 to 17 years living in the southeast and south-central United States. Cross-sectional serosurvey. Seven academic pediatric medical centers in the southeastern and south-central United States. Nineteen hundred ninety-nine children (approximately 300 at each center) having their blood drawn for any reason. The presence of antibody at 2 different cutoff titers to E chaffeensis, as detected by indirect immunofluorescence assay. Overall, 250 children (13%) had E chaffeensis antibody titers of 1:80 or higher and 61 (3%) had titers of 1:160 or higher. Age-adjusted seroprevalence rates varied widely between sites. At 1:80 or higher, the highest rate was in Winston-Salem, NC (22%), and the lowest was in Louisville, Ky (2%). At 1:160 or higher, the highest rate was in Kansas City, Mo (9%), and the lowest was in Oklahoma City, Okla (<1%). In univariate analyses, no associations were found between seroprevalence at either cutoff value and sex, race, source of specimen, or residence demographics. However, age was a significant predictor of seroprevalence at both cutoff values. In multiple logistic regression analysis, study site and age remained strong predictors of seroprevalence, but living in a nonurban ZIP code was not significantly related. Infection with E chaffeensis, or related ehrlichiae, may be more common in children than previously recognized.

Toxoplasma gondii infection in the United States: seroprevalence and risk factors.

Infection with Toxoplasma gondii can cause severe illness when the organism is contracted congenitally or when it is reactivated in immune-suppressed persons. To determine the prevalence of T. gondii infection in a representative sample of the US population, the authors tested sera from participants in the Third National Health and Nutrition Examination Survey (1988-1994) for immunoglobulin G antibodies to T. gondii. Of 27,145 persons aged > or =12 years, 17,658 (65%) had sera tested. The overall age-adjusted seroprevalence was 22.5% (95% confidence interval (CI): 21.1, 23.9); among women aged 15-44 years, seroprevalence was 15.0% (95% CI: 13.2, 17.0). Age-adjusted seroprevalence was higher in the Northeast (29.2%) than in the South (22.8%), Midwest (20.5%), or West (17.5%) (p < 0.05). In multivariate analysis, risk for T. gondii infection increased with age and was higher among persons who were foreign-born, persons with a lower educational level, those who lived in crowded conditions, and those who worked in soil-related occupations, although in subset analyses risk categories varied by race/ethnicity. Nearly one quarter of adults and adolescents in the United States have been infected with T. gondii. Most women of childbearing age in the United States are susceptible to acute infection and should be educated about ways to minimize exposure to T. gondii.

Effect of climatic factors and population density on varicella zoster virus epidemiology within a tropical country.

Blood samples were collected from healthy subjects, aged 9 months-29 years in urban and rural communities from 4 distinct regions in Thailand, to determine the seroprevalence rate of varicella-zoster virus (VZV) antibody and its relationship with demographic, climatic, and socioeconomic factors. The overall seroprevalence rate was 52.8% and increased from 15.5% in the 9-month to 4-year-old group to 75.9% in the 20-29 year-olds. The age-adjusted seroprevalence was significantly higher in the cooler than in the warmer regions. In the warmer regions only, the age-specific seroprevalence was significantly higher in the urban population than in the rural population. In Thailand, climate is the main determinant of VZV seroprevalence. The delayed onset of natural immunity is more marked in warmer climate areas. Population density is a secondary determinant; in the warmer areas, the pattern of adolescent and adult susceptibility was greater in rural than in urban areas.

HPV 16 antibody prevalence in Jamaica and the United States reflects differences in cervical cancer rates

Human papillomavirus (HPV) is widely accepted as the primary etiologic agent in the development of cervical cancer. DNA of a particular HPV type, HPV 16, is found in about half of tumors tested. Inconsistent with this causal relationship, however, population-based studies of HPV DNA prevalence have often failed to find high rates of anogenital HPV infection in countries with high cervical cancer rates. To examine this issue, we used serology to compare HPV 16 exposure in healthy volunteer blood donors in the United States (n = 278) and similar subjects from a country with 3-fold higher cervical cancer rates, Jamaica (n = 257). Jamaican sexually transmitted disease (STD) patients (n = 831) were also studied to examine in detail the relation of HPV 16 antibodies with sexual history. Serology was conducted using an ELISA employing HPV 16 virus-like particles (VLPs). Age-adjusted seroprevalence rates were greatest among male (29%) and female (42%) STD patients, intermediate in male (19%) and female (24%) Jamaican blood donors and lowest among male (3%) and female (12%) U.S. blood donors. The higher seroprevalence in women was significant, and prevalence tended to increase with age. In multivariate logistic regression, controlling for age and gender, Jamaican blood donors were 4.2-fold (95% CI 2.4–7.2) and STD patients 8.1-fold (95% CI 5.0–13.2) more likely to have HPV 16 VLP antibodies than U.S. blood donors. Among STD patients, HPV 16 antibodies were associated with lifetime number of sex partners and years of sexual activity, as well as other factors. Our data suggest that HPV 16 VLP antibodies are strongly associated with sexual behavior. Moreover, exposure to HPV 16 appears to be much greater in Jamaica than in the United States, consistent with the high rate of cervical cancer in Jamaica. Int. J. Cancer 80:339–344, 1999. Published 1999 Wiley-Liss, Inc.

Helicobacter antibodies in 1973 and 1994 in the adult population of Vammala, Finland.

Changes in Helicobacter pylori seroprevalence were studied determining IgG and IgA antibodies of 408 randomly selected adults aged 15-74 years living in Vammala, Finland in 1973 and of 504 similarly selected subjects in 1994. Seroprevalence increased by age at both time points. The age-adjusted seroprevalence rate was clearly lower in 1994 than in 1973 (31 vs. 56%, P = 0.001). Paired serum samples of 224 subjects collected in 1973 and 1994 showed that the antibody status remained unaltered in 92%; 4% seroconverted and 4% seroreverted within the 21 years. The decrease in the seroprevalence rate in the population and the persistence of individual antibody status over two decades support a difference in H. pylori infection rates among birth cohorts over time rather than continuous acquisition of new infections with advancing age. Thus the risk of helicobacter infection in Vammala, Finland has been highest in childhood and continuously decreased at least for the last five decades.

Sexual transmission of human T-lymphotropic virus type I (HTLV-I).

To study the seroprevalence of human T-lymphotropic virus type I (HTLV-I) in a sexually active population and to determine sexual behavior risk factors for infection. Cross-sectional seroprevalence study using enzyme-linked immunosorbent assay (ELISA) and Western blot. Risk-factor data were gathered by administered questionnaire and chart review. Two urban, primary care clinics for persons with sexually transmitted diseases run by the Jamaican Ministry of Health. Of the 2050 consecutive patients presenting with new episodes of sexually transmitted disease, 1977 patients were eligible for analysis. Overall HTLV-I seroprevalence was 5.7%; prevalence increased with age from 1.6% (age, 14 to 19 years) to 5.1% (age, 30 years and older) in men and from 5.3% (age, 14 to 19 years) to 14.1% (age, 30 years and older) in women. Compared with a reference cohort of food service employees, age-adjusted HTLV-I seroprevalence was increased in female patients with sexually transmitted disease (odds ratio = 1.83; CI, 1.41 to 2.83) but not in male patients with sexually transmitted disease. Independent risk factors for HTLV-I infection in women included having had more than ten lifetime sexual partners (odds ratio = 3.52, CI, 1.28 to 9.69) and a current diagnosis of syphilis (odds ratio = 2.12; CI, 1.12 to 3.99). In men, a history of penile sores or ulcers (odds ratio = 2.13; CI, 1.05 to 4.33) and a current diagnosis of syphilis (odds ratio = 3.56; CI, 1.24 to 10.22) were independent risk factors for HTLV-I infection. Of 1977 patients, 5 (0.3%) had antibodies to human immunodeficiency virus type 1 (HIV-1), including 2 with HTLV-I and HIV-1 coinfection. We conclude that HTLV-I is transmitted from infected men to women during sexual intercourse. Our data are consistent with the lower efficiency of female-to-male sexual transmission of HTLV-I, but penile ulcers or concurrent syphilis may increase a man's risk of infection.