Seroprevalence of latent cytomegalovirus infection among elderly Thais.

We determined the seroprevalence of latent cytomegalovirus (CMV) infection among young and elderly adults to test for a change in seroprevalence with increasing age. Thirty-two young and 32 elderly adults were tested for anti-CMV IgG, T-cell subgroup analysis, mental status and daily life activity. There was no significant difference in the seroprevalence of CMV infection between the two groups (59.4% vs 50.0%; p = 0.616). The subgroup analysis of T-cells showed significantly lower percentages of CD3 (64.5 +/- 9.5% vs 69.0 +/- 4.5%; p = 0.019) and CD8 (20.6 +/- 7.3% vs 28.3 +/- 6%; p < 0.001), and a higher percentage of CD4 (42.2 +/- 7.5% vs 36.5 +/- 4.7%; p = 0.001) cells in the elderly group. No differences in T-cell subgroups were observed by CMV serostatus subgroup among the young and elderly adult groups. Among the elderly there was a significantly lower mental status examination score among CMV positive subjects than CMV negative subjects (27.7 and 28.8 respectively, p = 0.049), but no difference in the advanced daily life activity index between the two groups. These results suggest the prevelence of CMV infection in elderly Thais does not increase with age and is not associated with immune status; however, the presence of latent CMV infection in the elderly may be associated with a decline in mental status, but not the inability to carry out activities of daily living. Further studies with large number of patients are needed to explore these findings.

Knowledge, attitudes, and acceptability of a human papilloma virus vaccine among students, parents and teachers in Thailand.

The purpose of this study was to assess the knowledge and attitudes about human papilloma virus (HPV) and cervical cancer, and the acceptability of HPV vaccine among students, parents and teachers in secondary schools in Bangkok, Thailand. We conducted a school-based cross-sectional study at four public secondary schools in Bangkok. A total of 644 students aged 12-15 years, 664 parents and 304 teachers were recruited into the study. Data were collected by self-administered questionnaires. The percentages of students, parents and teachers who were willing to be vaccinated were 26, 49 and 43%, respectively. Forty-one percent of parents wanted their children to be vaccinated. Students, parents and teachers had a moderate knowledge of HPV, cervical cancer and the HPV vaccine with mean scores of 6.91 (SD = 1.75), 6.82 (SD = 1.88), and 6.70 (SD = 1.89), respectively. The attitudes of students, parents, and teachers were fair with scores of 3.46 (SD = 0.41), 3.52 (SD = 0.43), and 3.46 (SD = 0.47) out of 5, respectively. Twenty-nine percent of students and 36% of parents were willing to pay USD 14.3-28.5 per dose for the quadrivalent vaccine; 33% of teachers were willing to pay < USD 14.3 per dose for the quadrivalent vaccine. This study is the first study to report the knowledge, and attitudes and acceptability of HPV vaccination in Thailand. The findings suggest the willingness to pay was relatively low and related to the price, while knowledge and attitudes regarding the importance of the HPV vaccine were fair particularly among parents and teachers. Greater effort may be needed to educate people regarding the cost and benefits of HPV vaccination before it would be more acceptable to parents, teachers and students in Thailand.

Predictive factors for Gnathostoma seropositivity in patients visiting the Gnathostomiasis Clinic at the Hospital for Tropical Diseases, Thailand during 2000-2005.

This was a retrospective study of patients having Gnathostoma antibody testing at the Hospital for Tropical Diseases, Bangkok during 2000-2005 to investigate predictive factors for Gnathostoma seropositivity in patients attending the Gnathostomiasis Clinic. Out of 849 patients tested, 531 (62.5%) were Gnathostoma seropositive. The median absolute eosinophil counts were 464 (0-16,796) and 326.5 (0-10,971) cells/mm3 in seropositive and seronegative patients, respectively (p<0.001). Differences in a history of cutaneous swelling, the habit of eating raw meat, eosinophilia (>500 cells/mm3), and the frequency of cutaneous swellings between seropositive and seronegative patients were all statistically significant. Patients with a history of eating raw meat and a history of cutaneous swelling were at 2.1 and 1.8 times more likely to be Gnathostoma seropositive, respectively. Logistic regression analysis showed eosinophilia was not a predictive factor for Gnathostoma seropositivity.

Knowledge, attitudes, and acceptability of a human papillomavirus vaccine among healthcare providers.

A cross-sectional survey was conducted to evaluate acceptability, knowledge, and attitude regarding HPV, cervical cancer, and HPV vaccine among healthcare providers working in hospitals located in Bangkok, Thailand. Two hundred nurses and 100 doctors from three government hospitals and one private hospital were recruited. Data collection was done using a self-administered questionnaire. Nurses and doctors knowledge on HPV, cervical cancer, and HPV vaccine was at a medium level. Both nurses and doctors had positive attitude toward HPV, cervical cancer, and HPV vaccine. Approximately 80% of nurses and 63% of doctors agreed on the use of a HPV vaccination. Almost all the nurses and doctors suggested that adolescent aged < or = 18-years-old should be the target group for HPV vaccination. Furthermore, 73% of nurses and 76% of doctors would recommend clients to receive HPV vaccine.

Social harms in injecting drug users participating in the first phase III HIV vaccine trial in Thailand.

OBJECTIVE: To study related social harms due to identification with a group of participants in an HIV-1 vaccine trial who are potentially high risk for HIV/AIDS. MATERIAL AND METHOD: Two thousand five hundred forty six injecting drug users (IDU) were enrolled in a 36-month vaccine trial. Volunteers received education and risk reduction counseling at every six-month study visit. Social harms were not actively solicited, but volunteers were encouraged to report any during the process of counseling at every six-month visit. If a social harm was reported, a questionnaire was administered and the harm was tracked If necessary, clinic staff assisted in resolving the social harm. RESULTS: Thirty-nine social harms were reported by 37 participants; 33 (84.6%) were disturbances in personal relationships, three (7.7%) in employment, one (2.6%) was medically related, one (2.6%) was related to admission in the military and one (2.6%) was related with misbelieve about the vaccine. The most common reason for disturbances in personal relationships was suspicion of HIV infection (n=20). The impact of these harms on quality of life was characterized as minimal by 31 (79.5%) participants, as moderate by seven (17.9%), and as major by one (2.6%). All social harms were documented to be resolved by the end of the study. CONCLUSION: A few participants reported study-related social harms during the course of the trial. Most harm had minimal impact and all could be resolved by the end of the present study.

Efficacy of ivermectin treatment of cutaneous gnathostomiasis evaluated by placebo-controlled trial.

Previous studies have revealed that ivermectin treatment for gnathostomiasis can reduce parasitic loads in animals and make recurrent subcutaneous swelling subside in 76% of patients. Our study aimed to evaluate the efficacy of ivermectin for cutaneous gnathostomiasis treatment in a placebo-controlled trial. This study was a prospective randomized placebo-controlled study performed at The Bangkok Hospital for Tropical Diseases, Mahidol University, Thailand. Thirty patients with a serologically confirmed diagnosis of cutaneous gnathostomiasis were enrolled. Seventeen patients in the ivermectin treated group received a single dose of 12 mg ivermectin (200 microg/kg bodyweight), while 13 patients in the control group received a single dose of 40 mg of vitamin B1. The follow-up period was 1 year. Of the 17 patients, 7 (41.2%) responded to ivermectin, while no patient responded to placebo. The mean (95% Cl) time to the first recurrence of subcutaneous swelling with ivermectin and in the placebo groups were 257 (184-331) and 146 (42-250) days, respectively, (p=0.102). Although this study revealed no significant difference in the mean time to first recurrence of swelling between the ivermectin and placebo groups, there was a trend towards ivermectin efficacy against gnathostomiasis in previous animal and human studies. Further studies with different doses of ivermectin and larger sample sizes, and close monitoring for ivermectin tolerability and treatment response are necessary to confirm an efficacy of ivermectin.

Tolerability of ivermectin in gnathostomiasis.

At present, no universally-accepted effective treatment for cutaneous gnathostomiasis is available. At the Hospital for Tropical Diseases, Mahidol University, albendazole 400 mg twice a day for 14 days is commonly prescribed for patients diagnosed with cutaneous gnathostomiasis. The efficacy of albendazole to induce outward migration of the parasite was less than or around 20% in 2 studies. Research for alternative, more efficacious treatment, is needed. In this prospective open-labeled study, we assessed the safety of ivermectin in 20 Thai patients diagnosed with cutaneous gnathostomiasis. Ivermectin, one time only, at dosages of 50, 100, 150, or 200 microg/kg bodyweight, was given orally to 4 groups of patients, 5 patients each group. Adverse events were recorded and laboratory tests were obtained before and after treatment. No serious adverse events occurred in this study. Forty adverse events were possibly related to ivermectin. The adverse events were malaise (35%), myalgia (30%), drowsiness (30%), pruritus (20%), nausea/vomiting (20%), dizziness (15%), diarrhea (15%), feeling of shortness of breath (10%), feeling of palpitations (10%), constipation (5%), anorexia (5%), and headache (5%). These adverse events were self-limited and not dose-related. Laboratory abnormalities were found in 3 patients (15%). Transient microscopic hematuria, pyuria, and mildly elevated liver enzymes were found in 1 patient each. Ivermectin single dose, of 50,100, 150, and 200 microg/kg bodyweight, is considered safe in Thai patients. Future trials of ivermectin on human gnathostomiasis may be performed using dosages up to 200 microg/kg bodyweight.

Association of intestinal helminths with decreased liver size and sCD23 concentration during falciparum malaria.

To determine if intestinal helminths and the CD23/nitric oxide pathway had an influence on liver size, we conducted a cross-sectional study on 438 patients with confirmed P. falciparum malaria admitted at the Hospital for Tropical Diseases in Bangkok. For all patients the liver size was measured as number of centimeters below the rib cage, a stool examination was conducted, and CD23 and reactive nitrogen intermediates were measured. The median liver size was smaller in helminth-infected patients than in helminth-free patients (chi2 for trend = 9.1, p = 0.003). Liver size significantly increased with the concentration of sCD23 (p < 0.0001). The median sCD23 concentration (OD) was significantly lower in helminth-infected patients than in helminth-free patients, respectively 0.33 (quartiles 0.24-0.57) and 0.45 (quartiles 0.27-0.59), (p = 0.01). There was a negative correlation between sCD23 concentrations and RNI (Spearman's rho = -0.40, p < 0.0001). All the above results remained significant after controlling for potential confounders. These results are compatible with a CD23/NO-mediated decrease in liver size in helminth-infected patients.

Mycobacterium tuberculosis infection among HIV/AIDS patients in Thailand: clinical manifestations and outcomes.

A one year retrospective study, was conducted at Bamrasnaradura Hospital, Nonthaburi Province, Bangkok, Thailand, of 271 subjects with both TB and HIV/AIDS. Single males (median age group 31 to 40 years) were most likely to develop co-infection. The commonest clinical manifestations on initial presentation included a low grade fever, cough, weight loss, lymphadenopathy with pancytopenia, and lung infiltrates. Multi-drug resistant TB (MDR-TB) was found in 26.6% of the subjects which was significantly associated with a past history of anti-TB treatment (p = 0.005; OR=2.5); it was also significantly associated with disseminated TB (p = 0.022; OR=1.9) and mortality (p= 0.013; OR=2.8). Analysis of clinical outcomes showed that 46.7% were lost to follow-up and 13.3% had died by the time of follow-up. Among those who survived, only 11.4% had been successfully treated; the rest had not improved due to relapse (2.9%), therapeutic failure (8.8%), treatment in progress (5.9%), and failure to complete treatment (10.7%).

6-month evaluation of JinHuang Chinese herbal medicine study in asymptomatic HIV infected Thais.

Good results of in vitro study of anti-HIV effects of JinHuang, a Chinese herbal medicine led to in vivo study of safety and efficacy among asymptomatic HIV infected individuals. It was a prospective open study of 21 asymptomatic HIV infected Thai volunteers. Twelve and 9 were female and male, respectively, with mean age of 29.24 +/- 3.94 years. JinHuang preparation, 6 capsules and 2 bottles of liquid formula orally three times a day, was given on an outpatient basis initially for 6 months. Regular close monitoring and follow-up were done. The side effects reported included : increased bowel movements (81%), vague taste, and smell of drug after initiation (52%). No serious adverse event related to JinHuang was detected during study. No significant changes in terms of log viral load and CD4 count were observed after 6-months' duration. Most of the patients felt that the quality of life was better in terms of better appetite, good sleep and healthy during study participation, however, these were subjective.

Clinical and mycological responses to fluconazole and fluconazole MIC in oropharyngeal candidiasis in HIV-infected patients.

INTRODUCTION: OPC is a common opportunistic infection in HIV-infected patients. Although some patients are asymptomatic, progression of the disease may occur leading to esophageal candidiasis. Fluconazole resistant candidiasis has been reported in several international studies. OBJECTIVES: This study aimed to test the MICs (minimal inhibitory concentrations) to fluconazole of Candida species isolated from mouthwash specimens of 54 HIV positive patients with oral candidiasis. Clinical and mycological responses to fluconazole were also assessed in 16 patients. MATERIAL AND METHOD: This was a prospective study. Mouthwash specimens were cultured on sabouraud dextrose agar twice. Candida species identification was performed and MICs for fluconazole were obtained using NCCLS guidelines. Clinical and mycological responses were assessed on day 14 and 42 in 16 patients who received a 14-day course of fluconazole. RESULTS: 48/54 patients (88.89%) were found to carry pure C. albicans. The other 6 patients (11.11%) had mixed Candida species on cultures. Among these 6 patients, 5 patients had mixed C. albicans and C. glabrata, and 1 patient had C. albicans and C. krusei. Fluconazole MICs of C. albicans, C. glabrata, and C. krusei ranged from 0.125-32 (median=0.250), 4-64 (median=2), and 8 g/L respectively. This study showed that the MICs to fluconazole of oropharyngeal Candida was a good predictor of the therapeutic responses.

Evaluation of attitude, risk behavior and expectations among Thai participants in Phase I/II HIV/AIDS vaccine trials.

The Understanding of volunteers in vaccine trials about their role as study participants and their voluntary commitment during the study are always one of the important concerns apart from evaluation of safety and efficacy of vaccine trials, especially in HIV prophylactic vaccine trials. The apprehension of indirectly risky behavior encouragement and deviated expectations among volunteers should be of concern. The current prospective cohort study aimed to assess and monitor the changes of risk behaviors, attitude and expectations among 164 volunteers from 2 studies of different prophylactic HIV vaccines, the Chiron HIV Thai E gp 120/MF59 +/- the Chiron HIV SF52 gp120 and Aventis Pasteur Live Recombinant ALVAC HIV (vCP1521) priming with VaxGen gp120B/E (AIDSVAX B/E) boosting. 113 males and 51 females with a mean age (+/- SD) of 28.82 +/- 7.97 years old were enrolled from October 1997 to December 1998 and February 2000 to April 2001. Education and risk reduction counseling were regularly performed at every visit and questionnaires about risk behaviors, knowledge, attitudes, social influences and expectations were asked at baseline, 4 months and 12 months. No change of potentially HIV transmission related risk behavior was observed during the studies. There was a statistically significant decrease of risk sexual practices from the beginning of the trials (42.2% vs 1%, p < 0.0001). While 35.2 per cent from 62.2 per cent of the volunteers at the beginning of the study continued sexual practice with an identified single sexual partner at the end of the study (p < 0.0001). All of the volunteers expressed the beneficial expectations as knowledge gain, social contribution, feelings of having gained merit and self-benefits from health check-ups.

Diagnosis of gnathostomiasis by skin testing using partially purified specific antigen and total IgE levels.

BACKGROUND: A finding of antibodies to Gnathostoma spinigerum 24-kDa antigen by immunoblot analysis is currently used to confirm a diagnosis of gnathostomiasis. A simple skin test for the diagnosis of gnathostomiasis was developed, and the results were evaluated and compared with the standard Western blot (WB) test. METHODS: This cross-sectional study was conducted at the Hospital for Tropical Diseases, Bangkok, Thailand, in 2008-2011. All eligible patients were tested with partially purified proteins of mAb-detected fractions pooled and sterilized by 0.2 µm diameter syringe filter, with a phenol saline solution of 1:10 w/v. RESULTS: A total of 69 cases, 39 gnathostomiasis cases and 30 controls, were enrolled into the study; the median age (IQR) was 40 (30.5-52.5) years. The most common presenting symptom was edema (56/69, 81%). Gnathostomiasis cases having strong cutaneous reactions to the intradermal test (81%) were also positive by immunoblot. A significant correlation between skin and immunoblot tests was detected (p<0.001). The difference in total IgE levels between cases and controls was not statistically significant (p=0.51). Logistic regression models showed that positive WB and skin-test results were significantly associated with gnathostomiasis (p=0.001 and p=0.007, respectively). CONCLUSION: Gnathostoma skin testing, using prepared fractionated antigen solution of Gnathostoma spinigerum, yields good reactivity and significantly correlates with the results of immunoblot testing.

Issues in women's participation in a phase III community HIV vaccine trial in Thailand.

To assess qualities and outcomes of women participating in a large, community-based HIV vaccine trial, the present study was conducted among female participants of the RV 144 prime-boost trial in Thailand from 2003 to 2009. Qualities of participation refer to complete vaccination, retention, and status change. Outcomes of participation refer to incident rate, adverse event, and participation impact event. A total of 6,334 (38.6%) women participated in the trial, of whom about 50% were classified as low risk and 11% as high risk. About 85% of participants completed four vaccinations and 76% were included in the per-protocol analysis of the on-time vaccination schedule. More women (88%) completed 42 months follow-up compared with men (85%). Women aged 21 and above had more adverse events compared to younger age groups. More women (5%) compared with men (3%) reported participation impact events (PIEs). High-risk women had more PIEs and a higher infection rate compared to the low-risk group. Complete vaccination and retention on last follow-up were more common in married women aged above 21, and being a housewife. Female volunteers showed the same qualities and outcomes of participation as males in the HIV vaccine trial. There was no statistically significant difference in vaccine efficacy between men and women, especially among the high-risk and married women. The study highlighted the important behavioral, social, and cultural issues that could be considered for future HIV vaccine trial designs.

Establishment of a Shigella sonnei human challenge model in Thailand.

In order to establish a human challenge model of Shigella related disease for vaccine testing, a dose-escalating inpatient trial was performed. Three groups of 12 healthy adult volunteers were orally challenged with 93,440 and 1680 CFU of Shigella sonnei strain 53G. Subjects were admitted to the Vaccine Trial Centre (VTC) at Mahidol University in Bangkok, Thailand. The primary purpose of this study was to identify the dose of S. sonnei 53G required to elicit clinical disease in at least 70% of Thai adult subjects. At the highest dose of 1680 CFU, the attack rate was 75%, while at the two lower doses, the attack rate was approximately 50%. This human challenge model, which is the first of its kind in an endemic region, will provide an opportunity for S. sonnei vaccine evaluation in endemic populations.

Measuring herpes zoster, zoster-associated pain, post-herpetic neuralgia-associated loss of quality of life, and healthcare utilization and costs in Thailand.

OBJECTIVES: This study aimed to measure the herpes zoster-associated burden of illness, healthcare utilization, and costs among Thai patients. METHODS: This prospective cohort study of 180 patients aged ≥ 50 years and healthy, or ≥ 20 years and immunosuppressed, with zoster rash, was conducted in Bangkok and its environs, Thailand, during 2007-2008. Each patient was followed for six months for zoster-associated rash, pain, quality of life (QoL), and healthcare utilization and costs. RESULTS: A total of 180 subjects were enrolled in the study. Their mean ± standard deviation (SD) age was 58.9 ± 13.8 years. Of the 180 patients enrolled, 138 (76.7%), 34 (18.9%) and eight (4.4%) patients were elderly, HIV-infected, and receiving immunosuppressive agents, respectively; 35 (19.4%) had post-herpetic neuralgia (PHN), and 13 (7.2%) had zoster ophthalmicus. The severity of zoster pain was moderately highly correlated with activities of daily living (ADL), at 0.68 ≤ ρ ≤ 0.76. Most patients required only one or two outpatient visits. The mean ± SD total of direct healthcare costs was 3083.4 ± 5047.0 Thai baht or ∼ 1.1% of annual income per capita. CONCLUSIONS: Herpes zoster contributes a significant burden of illness to both patients and the wider community.

Safety and reactogenicity of canarypox ALVAC-HIV (vCP1521) and HIV-1 gp120 AIDSVAX B/E vaccination in an efficacy trial in Thailand.

BACKGROUND: A prime-boost vaccination regimen with ALVAC-HIV (vCP1521) administered intramuscularly at 0, 4, 12, and 24 weeks and gp120 AIDSVAX B/E at 12 and 24 weeks demonstrated modest efficacy of 31.2% for prevention of HIV acquisition in HIV-uninfected adults participating in a community-based efficacy trial in Thailand. METHODOLOGY/PRINCIPAL FINDINGS: Reactogenicity was recorded for 3 days following vaccination. Adverse events were monitored every 6 months for 3.5 years, during which pregnancy outcomes were recorded. Of the 16,402 volunteers, 69% of the participants reported an adverse event any time after the first dose. Only 32.9% experienced an AE within 30 days following any vaccination. Overall adverse event rates and attribution of relatedness did not differ between groups. The frequency of serious adverse events was similar in vaccine (14.3%) and placebo (14.9%) recipients (p = 0.33). None of the 160 deaths (85 in vaccine and 75 in placebo recipients, p = 0.43) was assessed as related to vaccine. The most common cause of death was trauma or traffic accident. Approximately 30% of female participants reported a pregnancy during the study. Abnormal pregnancy outcomes were experienced in 17.1% of vaccine and 14.6% (p = 0.13) of placebo recipients. When the conception occurred within 3 months (estimated) of a vaccination, the majority of these abnormal outcomes were spontaneous or elective abortions among 22.2% and 15.3% of vaccine and placebo pregnant recipients, respectively (p = 0.08). Local reactions occurred in 88.0% of vaccine and 61.0% of placebo recipients (p<0.001) and were more frequent after ALVAC-HIV than AIDSVAX B/E vaccination. Systemic reactions were more frequent in vaccine than placebo recipients (77.2% vs. 59.8%, p<0.001). Local and systemic reactions were mostly mild to moderate, resolving within 3 days. CONCLUSIONS/SIGNIFICANCE: The ALVAC-HIV and AIDSVAX B/E vaccine regimen was found to be safe, well tolerated and suitable for potential large-scale use in Thailand. TRIAL REGISTRATION: ClinicalTrials.govNCT00223080.

Behavioral and social issues among volunteers in a preventive HIV vaccine trial in Thailand.

Behavioral and social issues were investigated in 363 phase I/II preventive HIV-1 vaccine trial volunteers in Thailand. These issues included risk behavior, HIV knowledge, distress, and social consequences of vaccine trial participation. Data were collected at baseline and at 4-, 8-, and 12-month follow-up visits. Volunteers reported relatively low levels of risk behaviors at baseline and at follow-up. Overtly negative reactions from family or friends were reported by 5.9%. No experiences of discrimination in employment, health care, or insurance were reported. Mean levels of distress were low throughout the trial, and HIV-related knowledge was high, although it was common to consider the possibility of HIV transmission through casual contact. Findings add to the evidence that preventive HIV vaccine trials are feasible in Thailand.

Safety and immunogenicity of an HIV subtype B and E prime-boost vaccine combination in HIV-negative Thai adults.

ALVAC-HIV (vCP1521) and AIDSVAX B/E were evaluated in a phase 1/2 trial of human immunodeficiency virus (HIV)-negative Thai adults. Of 133 volunteers enrolled, 122 completed the trial. There were no serious vaccine-related adverse events, nor were there intercurrent HIV infections. Lymphoproliferative responses to glycoprotein 120 E were induced in 63% of the volunteers, and HIV-specific CD8 cytotoxic T lymphocyte responses were induced in 24%. Antibody responses increased in frequency and magnitude in association with the dose level of AIDSVAX B/E. Binding and neutralizing antibodies to the MN strain were induced in 100% and 98%, respectively, of the volunteers receiving 600 microg of AIDSVAX B/E, and such antibodies to E strains were induced in 96% and 71%, respectively, of these volunteers. This vaccine combination was well tolerated and was immunogenic, meeting milestones for advancement to phase 3 evaluation.

Recruiting volunteers for a multisite phase I/II HIV preventive vaccine trial in Thailand.

Factors believed to be predictive of retention through the recruitment and screening processes for preventive HIV trials were investigated in a large multisite phase I/II HIV vaccine trial in Thailand. Retention through recruitment was equal to or greater than in previous smaller trials with similar populations. The data suggested that recruitment proceeded in a stepwise manner with different influences at each step. Demographic and motivational variables were most important in predicting retention in making and keeping screening appointments. Altruistic or mixed altruistic and nonaltruistic motives were associated with greater retention. Laboratory/medical variables appeared to be the main influence on retention during screening, although some volunteers withdrew for different reasons. The frequent presence of mixed (altruistic and nonaltruistic) motives at initial contact suggests that motivation for trials is more complex than has been previously acknowledged.