Estimating the risk of dengue transmission from Dutch blood donors travelling to Suriname and the Dutch Caribbean

BACKGROUND

The risk of dengue transmitted by travellers is known. Methods to estimate the transmission by transfusion (TT) risk from blood donors travelling to risk areas are available, for instance, the European Up-Front Risk Assessment Tool (EUFRAT). This study aimed to validate the estimated risk from travelling donors obtained from EUFRAT.

METHODS

Surveillance data on notified dengue cases in Suriname and the Dutch Caribbean islands (Aruba, Curaçao, St. Maarten, Bonaire, St. Eustatius and Saba) in 2001-2011 was used to calculate local incidence rates. Information on travel and donation behaviour of Dutch donors was collected. With the EUFRAT model, the TT risks from Dutch travelling donors were calculated. Model estimates were compared with the number of infections in Dutch travellers found by laboratory tests in the Netherlands.

RESULTS

The expected cumulative number of donors becoming infected during travels to Suriname and the Dutch Caribbean from 2001 to 2011 was estimated at 5 (95% CI, 2-11) and 86 (45-179), respectively. The infection risk inferred from the laboratory-based study was 19 (9-61) and 28 (14-92). Given the independence of the data sources, these estimates are remarkably close. The model estimated that 0·02 (0·001-0·06) and 0·40 (0·01-1·4) recipients would have been infected by these travelling donors.

CONCLUSIONS

The EUFRAT model provided an estimate close to actual observed number of dengue infections. The dengue TT risk among Dutch travelling donors can be estimated using basic transmission, travel and donation information. The TT risk from Dutch donors travelling to Suriname and the Dutch Caribbean is small.

HIV testing behaviour among heterosexual migrants in Amsterdam

This cross-sectional study among heterosexual migrant groups in south-eastern Amsterdam, the city area where the largest migrant groups live, provides an insight into HIV testing behaviour in this particular group. Participants were recruited at street locations (May 1997-July 1998) and interviewed using structured questionnaires. They also donated saliva for HIV testing. In total, 705 males and 769 females were included in this study (Afro-Surinamese (45%), Dutch-Antilleans (15%) and West Africans (40%)). Prior HIV testing was reported by 38% of all migrants (556/1479), of which only a minority (28%) had actively requested HIV testing. Multivariate logistic regression showed that not actively requesting HIV testing was more likely among younger (< 23 years) migrants, especially women (ORwomen: 4.79, p < 0.01, ORmen: 1.81, p < 0.05). Furthermore, women without previous STI treatment (OR 2.19, p < 0.05) with Afro-Surinamese ethnicity (OR 2.12, p < 0.05), men without health insurance (OR 2.17, p < 0.05) and with low education (p < 0.01) were also more likely to not actively request HIV testing. Active requests for HIV testing in case of HIV risk should be facilitated by promoting HIV testing and by improving accurate self-assessment of risk for HIV infection, especially among the groups that do not actively request HIV testing. This would increase HIV awareness and provide the opportunity of better medical care earlier in HIV infection.

Evaluation of a risk assessment questionnaire to assist hepatitis C screening in the general population

Many individuals with hepatitis C virus (HCV) infection are undiagnosed. This study evaluates a risk assessment questionnaire, developed for use online to target blood-screening for HCV. Two hundred and eighty-nine patients with known HCV status completed a written questionnaire on prominent HCV risk factors. Questionnaires generated advice to seek testing if at least one risk factor was reported. Agreement of the testing advice with the HCV status of respondents was evaluated. Subsequently, we validated our questionnaire among 985 patients of an outpatient clinic for sexually transmitted infections. The post-test-probability-of-disease (PTPD) and diagnostic gain (PTPD minus prior probability of disease) were calculated. The questionnaire's sensitivity and specificity were 84.6% and 63.8%, respectively, and higher in the STI clinic patients. The PTPD of positive testing advice was 72.5% given HCV prevalence of 53.0%, yielding a diagnostic gain of 19.5%. Applying the estimated prevalence in the general Dutch population (0.1-0.4%), and the anticipated prevalence in the online project (1.0-6.0%), yielded diagnostic gains of 0.13-0.53% and 1.3-7.0%, respectively. We conclude that our questionnaire succeeded in selecting at-risk individuals as its testing advice agreed well with the HCV status. We suggest that the questionnaire be used online as a selection tool for HCV blood-screening in the general population.

Ongoing transmission of a single hepatitis B virus strain among men having sex with men in Amsterdam

For the past decade, a specific hepatitis B virus (HBV) genotype A strain has been prevalent among men having sex with men (MSM) in Amsterdam, the Netherlands. At what point in time this strain was introduced in the MSM population, and why only this specific strain continues to be transmitted, remains unclear. Between 1984 and 2003, sera of 1862 MSM were retrospectively screened for anti-HBc in the context of the Amsterdam Cohort studies. After 2003, most MSM participating in this study were vaccinated, making further testing less useful. HBV DNA from anti-HBc seroconverters was amplified and sequenced. Poisson regression was used to test for temporal trends in HBV and HIV incidence. Of the 1042 MSM who were negative for anti-HBc at entry, 64 had seroconverted during follow-up at a median age of 32. At the point of seroconversion, 31 MSM were HIV positive. HBV incidence declined dramatically in the first years and then remained stable throughout the study period. The HBV and HIV incidence ran almost in parallel. With the exception of three MSM, all were infected with genotype A. Fifteen of these (41%) were infected with an identical genotype A strain. For the past two decades, an identical genotype A strain has been circulating among MSM in the Netherlands. Although HBV is generally considered more infectious than HIV, this study shows that the trend and magnitude in HBV and HIV incidence among MSM are similar.

Disassortative sexual mixing among migrant populations in The Netherlands: a potential for HIV/STI transmission?

To gain insight into the transmission of HIV and sexually transmitted infection (STI) among large migrant groups in The Netherlands, we studied the associations between their demographic and sexual characteristics, in particular condom use, and their sexual mixing patterns with other ethnic groups. In 2002-2005, cross-sectional surveys were conducted among migrants from Surinam (Afro- and Hindo-), the Netherlands Antilles, Cape Verde, and Ghana at social venues in three large cities. A questionnaire was administrated and a saliva sample was collected for HIV antibody testing. Of 2105 migrants recruited, 1680 reported sexual contacts, of whom 41% mixed sexually with other ethnicities, including the indigenous Dutch population. Such disassortative mixing was associated with being second-generation migrant, having several sexual partners, and having a steady and concurrent casual partner. Less disassortative mixing occurred in participants reporting visiting the country of origin. The association between condom use and sexual mixing differed by gender, with men using condoms inconsistently being most likely to be mixing with the Dutch indigenous population. HIV infection and recent STI treatment were not associated with disassortative mixing. This study shows substantial sexual mixing among migrant groups. Since disassortative mixing is more prevalent in second-generation migrants, it might increase in the upcoming years. The mixing patterns in relation to concurrency and the reported condom use in this study suggest a possibly increased level of HIV/STI transmission not only within migrant groups but also between migrant groups, especially via men who mix with the indigenous population and via migrant women who mix with non-Dutch casual partners. Although the observed HIV prevalence in migrants (0.6%) is probably too low to lead to much HIV transmission between ethnicity groups, targeted prevention measures are needed to prevent transmission of other STI.

Never injected, but hepatitis C virus-infected: a study among self-declared never-injecting drug users from the Amsterdam Cohort Studies

The aim of this study was to gain insight in transmission routes of hepatitis C virus (HCV) infection among never-injecting drug users (DU) by studying, incidence, prevalence, determinants and molecular epidemiology of HCV infection. From the Amsterdam Cohort Studies among DU, 352 never-injecting DU were longitudinally tested for HCV antibodies. Logistic regression was used to identify factors associated with antibody prevalence. Part of HCV NS5B was sequenced to determine HCV genotype and for phylogenetic analyses, in which sequences were compared with those from injecting DU. HCV antibody prevalence was 6.3% and HCV incidence was 0.49/1000 PY. HIV-positive status, female sex and starting injection drug use during follow-up (a putative marker of past injection drug use), were independently associated with HCV prevalence. The main genotypes found were genotype 3a (50%) and 1a (30%). Phylogenetic analysis revealed that HCV strains in never-injecting DU did not cluster together and did not differ from HCV strains circulating in injecting DU. We found a higher HCV prevalence in never-injecting DU than in the general population. Phylogenetic analysis shows a strong link with the injecting DU population. The increased risk could be related to underreporting of injecting drug use or to household or sexual transmission from injectors to noninjectors. Our findings stress the need for HCV testing of DU who report never injecting, especially given the potential to treat HCV infection effectively.

Second national serum bank for population-based seroprevalence studies in the Netherlands

In 2006/2007 a large serum bank was established by means of a cross-sectional population-based study. This serum bank will be used to evaluate the Dutch national immunisation programme (NIP) by serosurveillance and additional immunological and epidemiological research. In this paper we describe the design of this population-based cross-sectional serosurvey and report the participation rates as well as general characteristics of the study population. A similar serum bank was collected in 1995/1996. Dutch inhabitants (aged 0-79 years, men and women) were invited from 40 municipalities throughout the country and also from eight additional municipalities known with low vaccination coverage (LVC). An oversampling of the migrant population was performed. Blood samples were obtained from all participants accompanied with extensive information on demographic and epidemiological data, such as vaccination history, risk factors and travelling. In addition, sociodemographic data are available from individuals who declined to participate (non-response survey). Overall 33% of all invitees were included in this study. The serum bank comprises 6386 sera in the nationwide sample including the extra sample of immigrants (n=646) and 1518 sera from the LVC municipalities. The sera will be analysed for antibodies against all NI P antigens but will also be used for other infectious diseases research. Results of this second serosurveillance study will contribute to the discussion whether it is needed to reconsider the schedule and/or the vaccine components of the current National Immunisation Programme.

TprK gene regions are not suitable for epidemiological syphilis typing

Given reports of increasing syphilis incidence in Western countries, we used molecular typing and epidemiological data to elucidate Treponema pallidum transmission networks. Samples and data were collected, dating from 2002 to 2005, from a well-defined population of patients with an ulcus and a diagnosis of infectious syphilis. Molecular typing using the tprK gene (V3-V5 region) was performed on 211 isolates from 205 Amsterdam STI clinic patients. We revealed 32 T. pallidum clusters and recognized ten large clusters, consisting predominantly of homosexual men (89%). Yet, no common patient characteristics were found to link the patients in these clusters. We therefore conclude that the highly variable tprK region (V3-V5) is not suitable for elucidating T. pallidum transmission networks in a high risk population.

[Hepatitis B virus transmission patterns in the Netherlands, 2004]

OBJECTIVE

To gain insight into hepatitis B virus (HBV) transmission in the Netherlands.

DESIGN

Descriptive.

METHOD

During 2004, epidemiological data and blood samples (if available) were collected for all reported cases of acute HBV infections in the Netherlands. Following DNA isolation and amplification a 648 base pairs fragment of the HBV S gene was sequenced and subjected to phylogenetic analysis. The sequencing details were also linked to epidemiological information.

RESULTS

In 2004, 291 cases ofacute HBV infections were reported. Blood samples were received from 171 patients (59%), and the genotype could be determined for 158 patients (54%). 6 genotypes were identified: A (64%), B (3%), C (3%), D (21%), E (5%) and F (4%). Of all patients with genotype A, 52% had been infected via homosexual or bisexual contact and 16% via heterosexual contact. Of all patients with genotype D, 42% had been infected via heterosexual contact and 15% via homosexual or bisexual contact. The genotype A cluster was extremely homogeneous with many identical sequences, while genotype B-E clusters were more heterogeneous. 4 identical sequences were found within genotype F, but the patients could not be epidemiologically linked.

CONCLUSION

Sexual transmission, particularly via homosexual or bisexual contact in men, formed the most important risk factor for acquiring an acute HBV infection. Genotype A was predominant in the Netherlands, especially among homosexual or bisexual men. Most infections within genotype D occurred as a result of heterosexual contact. The results show that there was ongoing transmission of HBV in homosexual or bisexual men, while in heterosexuals more cases of new introduction were seen, possibly via chronic carriers from areas where HBV is endemic.

Changes in prevention and outbreak management of Legionnaires disease in the Netherlands between two large outbreaks in 1999 and 2006

We describe an outbreak of Legionnaires' disease in 2006 in Amsterdam, the Netherlands. Comparisons with the outbreak that took place in 1999 are made to evaluate changes in legionella prevention and outbreak management. The 2006 outbreak was caused by a wet cooling tower. Thirty-one patients were reported. The outbreak was detected two days after the first patient was admitted to hospital, and the source was eliminated five days later. The 1999 outbreak was caused by a whirlpool at a flower show, and 188 patients were reported. This outbreak was detected 14 days after the first patient was admitted to hospital, and two days later the source was traced. Since 1999, the awareness of legionellosis among physicians, the availability of a urinary antigen tests and more efficient early warning and communication systems improved the efficiency of legionellosis outbreak management. For prevention, extensive legislation with clear responsibilities has been put in place. For wet cooling towers, however, legislation regarding responsibility and supervision of maintenance needs to be improved.

Migrants travelling to their country of origin: a bridge population for HIV transmission?

BACKGROUND

By having unprotected heterosexual contact in both The Netherlands and their homeland, migrants who travel to their homeland might form a bridge population for HIV and sexually transmitted infection (STI) transmission. We studied the determinants for such a population in two large migrant communities in The Netherlands.

METHODS

From 2003 to 2005, 1938 people of Surinamese and Antillean origin were recruited at social venues in two large cities, interviewed and their saliva samples tested for HIV antibodies. We used multivariate multinomial logistic regression to explore characteristics of groups with four risk levels (no, low, moderate and high) for cross-border transmission.

RESULTS

1159/1938 (60%) participants had travelled from The Netherlands to their homeland in the previous 5 years and 1092 (94%) of them reported partnerships and condom use in both countries. Of these 9.2% reported having unprotected sex with partners in both countries. People in this high-risk or bridge population group were more likely to be male, frequent travellers and older compared with people who had no sex or had sexual contact solely in one country in the past 5 years.

CONCLUSIONS

Older male travellers of Surinamese and Antillean origin are at high risk for cross-border heterosexual transmission of HIV/STIs. They should be targeted by prevention programmes, which are focused on sexual health education and HIV/STI testing, to raise their risk awareness and prevent transmission.

Ethnic differences in HSV1 and HSV2 seroprevalence in Amsterdam, the Netherlands

Herpes simplex virus type 1 (HSV1) and 2 (HSV2) infection can lead to significant morbidity, and HSV2 is considered a risk factor for HIV transmission. The majority of HSV-infected people are asymptomatic and unaware of their infection. We aimed to determine the HSV1 and HSV2 prevalence among various ethnic groups in a large urban area in the Netherlands. In 2004, serum samples from a population-based serum repository of 1,325 people over 18 years living in Amsterdam were tested for HSV1 and HSV2 antibodies in order to determine high-risk groups. Prevalence ratios were estimated and all analyses were weighted by sex, age, and ethnicity. In the general population of Amsterdam, 67% had HSV1 antibodies, 22% had HSV2 antibodies, 15% had HSV1 and HSV2 antibodies, and 26% had no indication of HSV infection. In multivariate analyses, HSV1 seroprevalence increased with age, and was higher among people of Turkish and Moroccan origin, homosexual men, and individuals with low educational level. HSV2 seroprevalence was associated with increasing age, Surinamese/Antillean background, and having a history of sexually transmitted infections (STI). These differences between ethnic groups in Amsterdam regarding the distribution of HSV1 and HSV2 infection emphasise the importance of an ethnic-specific approach of serological testing as well as campaigns aimed at behavioural change and counselling to raise awareness of the risk of HSV transmission.

[The molecular epidemiology of hepatitis A in The Netherlands; the usefulness of typing isolated viral strains]

OBJECTIVE

To investigate the epidemiological links between several outbreaks of hepatitis A in The Netherlands (2001-2004).

DESIGN

Descriptive.

METHOD

Blood samples taken in connection with reports of hepatitis A to municipal health centres from 2001-2004, were typed by determining the nucleotide sequence of the VP3-VP1 and the VP1-P2A regions of the genome of the hepatitis A virus (HAV). Genetic distances were represented graphically by means of a phylogenetic tree.

RESULTS

The study into the spread of various subtypes of HAV showed a clear link between the HAV-(sub)genotype and risk of transmission: in men that have sex with men only genotype 1A occurred, in travellers to African countries genotype 1B was predominantly seen.

CONCLUSION

A database containing various viral strains from people with hepatitis A in The Netherlands could, if kept up to date, be used as an aid in confirming the classical way of tracing sources as well as for the evaluation of preventative measures.

Population-based study on the seroprevalence of hepatitis A, B, and C virus infection in Amsterdam, 2004

In order to enhance screening and preventive strategies, this study investigated the seroprevalence of hepatitis A, B, and C in the general adult urban population and in subgroups. In 2004, sera from 1,364 adult residents of Amsterdam were tested for viral markers. Sociodemographic characteristics were collected using a standardized questionnaire. For hepatitis A, 57.0% was immune. Of first-generation immigrants from Turkey and Morocco, 100% was immune. Of all Western persons and second-generation non-Western immigrants, approximately half was still susceptible. For hepatitis B, 9.9% had antibodies to hepatitis B core antigen (anti-HBc) and 0.4% had hepatitis B surface antigen. Anti-HBc seroprevalences were highest among first-generation immigrants from Surinam, Morocco, and Turkey, and correlated with age at the time of immigration, and among men with a sexual preference for men. Seroprevalence among second-generation immigrants was comparable to Western persons. The seroprevalence of hepatitis C virus antibodies was 0.6%. In conclusion, a country with overall low endemicity for viral hepatitis can show higher endemicity in urban regions, indicating the need for differentiated regional studies and prevention strategies. More prevention efforts in cities like Amsterdam are warranted, particularly for hepatitis A and B among second-generation immigrants, for hepatitis B among men with a sexual preference for men, and for hepatitis C. Active case finding strategies are needed for both hepatitis B and C.

[High time for wide application of an opting-out strategy for HIV testing]

--Despite the current active HIV test policy, the effects of the former policy are still visible, i.e. a relatively low number of individuals that have ever been tested for HIV. --The number of HIV tests and knowledge of current HIV status has increased among visitors to the STI clinic in Amsterdam. --Nevertheless, anonymous HIV surveillance among visitors to the STI clinic shows that a considerable proportion of HIV-infected individuals (24% of men who have sex with men (MSM) and 80% of heterosexuals) are unaware of the infection. --A new opting-out strategy for HIV testing in STI clinics is recommended. --The opting-out strategy may also be applicable to other medical settings, especially those that treat target populations such as MSM, heterosexuals with STI-related symptoms, and persons originating from AIDS-endemic regions. --The opting-out system was initiated in the Amsterdam STI clinic in 2007 in order to further reduce the number of undiagnosed HIV infections.

[Do not forget HIV in the Netherlands]

At the time of the first aids cases in 1981 in the United States, no one could have predicted that it would signal the start of a worldwide epidemic. To mark World Aids Day, this journal is devoting a special issue to HIV/AIDS. Erroneously, it seems that in the Netherlands HIV/AIDS is sometimes forgotten. Among men who have sex with men, the HIV incidence is around 1%--a rate that is just as high as that among adults in many African countries. In order to slow down the spread of the virus, there should be more intensive testing for HIV, by, for example, 'opting out'. Developments in the field ofHIV/AIDS outside the Netherlands are also discussed. There is an article on a successful HIV/AIDS treatment project setup by Médicins sans Frontières in the Ukraine. The consequences of the large-scale availability of antiretroviral drugs in developing countries are also examined. Because of these programs increased resistance of the virus to the medication may become a problem. Further, a promising initiative to improve the financing of healthcare systems in Africa is discussed. An effective vaccine for HIV seems far away. Recently, Merck halted the development of an HIV vaccine based on T cell immunity, because the clinical results were disappointing. Waning interest in investing in an HIV vaccine from the pharmaceutical sector means that governments will have to increasingly take on this role. For now strategies for the prevention of HIV must be to continue to stimulate safe sexual behavior, good diagnostic and treatment services for sexually transmitted infections, and more and earlier HIV testing.

[Hepatitis C in the Netherlands: sparse data on the current prevalence and the necessity for epidemiological studies and innovative methods for detecting infected individuals]

Hepatitis C is a blood-borne virus infection with an estimated 180 million infected individuals worldwide. Hepatitis C virus (HCV) infection may lead to liver failure and cancer of the liver. In 2004, in view of the improved treatment options, the Dutch Health Council again recommended that the groups at risk of HCV infection should be tracked down and informed, and that epidemiological studies should be conducted. Currently, there are few data on the prevalence of HCV infection in the Netherlands. HCV risk groups are (former) injecting drug users, haemodialysis patients and haemophiliacs, people treated with blood or blood products before 1992, people who have undergone certain invasive or medical procedures with insufficiently sterilised instruments, household contacts and partners of HCV-infected individuals and children born to HCV-infected mothers. Insight into the epidemiology of HCV infection in the Netherlands is necessary so that reliable estimates of the magnitude of hepatitis C as a public health problem can be made. Several projects for the detection of HCV infected individuals and epidemiological studies have started in 2007.

[Adverse events following influenza vaccination: reaction to specific reports and the necessity of a central registration system]

The influenza vaccine is considered safe, but information on vaccine-related adverse events is limited and a nationwide overview of adverse events is lacking. In 2006, after deaths occurred in Israel and the Netherlands following influenza vaccination, the Dutch Ministry of Health, Welfare and Sport (VWS) asked the National Institute for Public Health and the Environment (RIVM) twice for a recommendation regarding the continuation of the national vaccination campaign. After 4 deaths were reported in Israel in October 2006 following administration of Vaxigrip, the Dutch vaccination campaign was suspended for one week. One month later, 4 additional deaths were reported after influenza vaccination in the Netherlands. The newly appointed outbreak management team concluded that a causal relationship between vaccination and the deaths was highly unlikely, based on data regarding the individual cases, background mortality rates and prior reports of adverse events. Further suspension of the vaccination campaign was deemed unnecessary this time. A centralised nationwide registry of adverse events has since been established to provide further insight into the incidence of adverse events following influenza vaccination. Physicians are advised to report potential adverse events following influenza vaccination to the Netherlands Pharmacovigilance Centre Lareb (www.lareb.nl).

Molecular epidemiology of acute hepatitis B in the Netherlands in 2004: nationwide survey

To gain insight into hepatitis B virus (HBV) transmission in the Netherlands, epidemiological data and sera were collected from reported cases of acute HBV infections in the Netherlands in 2004. Cases were classified according to mode of transmission. A fragment of the S-gene of HBV (648 bp) was amplified, sequenced, and subjected to phylogenetic analysis. Of the 291 acute HBV cases reported in 2004, 158 (54%) were available for genotyping. Phylogenetic analysis identified 6 genotypes: A (64%), B (3%), C (3%), D (21%), E (5%) and F (5%). Of HBV infected men having sex with men, 86% were infected with genotype A, accounting for 43% of all patients infected with this genotype. There were only three reported cases of injecting drug use of which one was available for sequencing (genotype A). Unlike the genotype A cluster, sequences within the genotype B-E clusters were heterogenic. Within genotype F, several isolates had identical sequences, but patients could not be epidemiologically linked. Sexual transmission, particularly by men having sex with men was the most important transmission route for HBV. Injecting drug use plays a minor role. Genotype A is predominant in the Netherlands, especially among men having sex with men. In addition to imported strains, there seems to be a pool of related but non-identical strains circulating among chronic carriers in the migrant population, from which occasionally new patients are infected, primarily by heterosexual transmission.

[Combating infectious disease using mathematical modelling]

When determining interventions against threatening infectious diseases such as HIV-infection, severe acute respiratory syndrome (SARS), smallpox and pandemic influenza, the use of mathematical models of the spread of infectious diseases is becoming increasingly popular. These models contribute to the structuring of the knowledge already available in various disciplines, to finding epidemiological connnections, to demonstrating lacunas within the pool of knowledge and to the comparison of the expected effects and costs of preventative and intervention measures. The use of models leads to a 'made-to-measure' analysis ofthe effects and costs of preventative and intervention measures which takes account of the specific characteristics of infectious diseases. The integration of knowledge from various disciplines can be supported by more research into the theoretical epidemiology of infectious disease and by better integration of mathematical models into policy development. The resulting and better foundations of this policy that are achieved by means of infectious disease modelling translate into more effective combating of infectious disease.

[Legionella outbreak in Amsterdam: a cooling tower as the source]

During the period 6-28 July 2006, 30 confirmed cases of Legionella infection were identified in Amsterdam, 2 of which were fatal. All had a positive urinary antigen test, by which Legionella pneumophila serogroup I could be demonstrated. Consultations between the parties involved in the control of infectious diseases started on July 7th, as soon as it became clear that there was an outbreak. On July 10th it was established that relatively many of these patients lived in the eastern part of the city centre. After a study of the prevailing winds during the past 3 weeks, the search for installations containing water was started. A cooling tower in the town centre was closed on July 11th by way of precaution. During the following week, this tower was proven to be the source of the outbreak.

Effectiveness of a hepatitis A vaccination program for migrant children in Amsterdam, The Netherlands (1992-2004)

OBJECTIVE

To evaluate the impact and effectiveness of risk-group vaccination against hepatitis A targeted at migrant children living in a country with low endemicity of hepatitis A.

METHODS

Retrospective population based data analysis. Routinely collected data on hepatitis A incidence in migrant children and other risk groups in Amsterdam from 1 January 1992 to 2004 were analyzed and related to exposure, immunity and vaccination coverage in migrant children.

RESULTS

The overall hepatitis A incidence in Amsterdam declined after a pediatric vaccine was introduced in 1997. This decline was seen in migrant children traveling to hepatitis A-endemic countries, contacts with hepatitis A patients, primary school students, injecting drug users, and persons with unknown source of infection, but not in men who have sex with men (MSM) or in travelers to endemic countries other than migrant children.

CONCLUSION

The hepatitis A vaccination campaigns are effective: they reduce both import and secondary HAV cases. The campaigns could be more efficient and cost-effective if the hepatitis B vaccinations currently given to these groups were replaced by a combined hepatitis A and B vaccine. This would increase the hepatitis A vaccination coverage considerably and further reduce the hepatitis A incidence.

Tattooing, permanent makeup and piercing in Amsterdam; guidelines, legislation and monitoring

Tattooing, body piercing and permanent makeup are increasing in popularity. Here, we describe the procedures involved in these practices, their risks, the content of guidelines developed by the Municipal Health Service in Amsterdam (the Netherlands) to reduce infection risks, the legislation in the city of Amsterdam, and results of monitoring in tattoo and piercing studios.

Tattooing, permanent makeup and piercing in Amsterdam; guidelines, legislation and monitoring

Tattooing, body piercing and permanent makeup are increasing in popularity. Here, we describe the procedures involved in these practices, their risks, the content of guidelines developed by the Municipal Health Service in Amsterdam (the Netherlands) to reduce infection risks, the legislation in the city of Amsterdam, and results of monitoring in tattoo and piercing studios.

Sexual risk behaviour among Surinamese and Antillean migrants travelling to their countries of origin

OBJECTIVES

To examine travel related sexual risk behaviour among migrants living in Amsterdam.

METHODS

People originating from Surinam (n = 798) and the Netherlands Antilles (n = 227) were recruited in order to study the heterosexual spread of HIV within ethnic groups. Log binomial regression was used to study determinants for homeland travel over the past 5 years; logistic regression was used to study determinants of unprotected sex on these visits.

RESULTS

Of the migrants, 38% of men and 42% of women visited their homeland. Visits were most likely among men who had lived > or =7 years in the Netherlands, were employed, had a high educational level and were/had been married. For women, visiting was associated with older age and living in the Netherlands for > or =8 years. Of migrants visiting their homeland, 47% of men and 11% of women acquired a local sexual partner. For male travellers, Surinamese origin (adjusted OR 10.66; 95% CI 1.72 to 104.48) and a history of > or =1 sexually transmitted infection (STI) (adjusted OR 12.51; 95% CI 3.75 to 46.95) were associated with having unprotected sex with local partners. For women, having >1 partner in the past 5 years (OR 13.57; 95% CI 2.57 to 250.28) was associated with unprotected sex with local partners.

CONCLUSION

Migrants are at substantial risk for HIV and STIs while visiting their homeland. It is important to reach migrants, who are likely to engage in unprotected sex during visits, for pretravel health education. Additional research on risk behaviour in the homeland and the Netherlands is needed to identify migrants with high risk behaviour.

[Avian influenza H5NI in Europe: little risk as yet to health in the Netherlands]

Since 2004, outbreaks of fowl plague caused by a highly pathogenic avian influenza virus of the subtype A/H5NI have been reported from various countries in Southeast Asia. To date, 118 cases with 61 deaths have been documented in humans, due to close contact with infected poultry or raw poultry meat. Although efficient human-to-human transmission has not occurred, in a few cases transmission to blood relatives could not be ruled out. In October 2005, outbreaks of A/H5NI in poultry and wild fowl have been confirmed from Turkey, Romania and Russia, due probably to infection via migratory birds. The direct risk of infection in humans in Europe is very low and is associated with direct exposure to infected poultry. In order to address the long-term risk of a pandemic due to recombination of human and avian viruses or to mutations in the avian virus itself, guidelines for pandemic preparedness have been developed and implemented in the Netherlands.

Molecular epidemiology of hepatitis A in Noord-Brabant, The Netherlands

BACKGROUND

Previous studies on the molecular epidemiology of hepatitis A virus (HAV) in Amsterdam, The Netherlands, show that subgenotype 1A is mainly seen among homosexual men practising anonymous oral-anal sex in saunas and darkrooms, while subgenotype 1B is usually detected among children originating from Morocco, and subgenotype 3A is mostly found among travellers to Pakistan.

OBJECTIVE

We studied the genotype distribution in a more rural area of The Netherlands, Noord-Brabant, and compared it with Amsterdam.

STUDY DESIGN

We collected blood and feces samples from 34 HAV IgM(+) individuals who were reported from August 2001-March 2003 at the Municipal Health Service (MHS) Heart for Brabant (Brabant). We also collected feces samples from nine household contacts of whom the HAV IgM status was not known. HAV RNA was isolated and subsequently amplified by reverse transcriptase polymerase chain reaction (RT-PCR) at the VP1-P2a and the VP3-VP1 region, sequenced and analysed.

RESULTS AND CONCLUSIONS

In most cases, relations between risk groups and HAV subgenotypes in Noord-Brabant were similar to those in Amsterdam. Next to genotypes 1 and 3 we also detected a genotype 2/7 strain in a Noord-Brabant case. Also, in contrast to the Amsterdam study, sporadic transmission occurred among various risk groups. Children involved in a school-related outbreak were infected with strains identical to one that was previously isolated from a man who has sex with men (MSM). Also, Dutch patients having no epidemiological link with Turkish or Moroccan children harboured strains imported from high-endemic countries. Furthermore, we report a special case in which HAV may be causally involved in meningitis. The results of this study show that the molecular epidemiology of HAV in The Netherlands can be more complicated than previously anticipated and that HAV phylogenetic studies can provide important information for the design of appropriate public health measures.

Increase of sexually transmitted infections, but not HIV, among young homosexual men in Amsterdam: are STIs still reliable markers for HIV transmission?

OBJECTIVES

The incidence of HIV and STIs increased among men who have sex with men (MSM) visiting our STI clinic in Amsterdam. Interestingly, HIV increased mainly among older (> or =35 years) MSM, whereas infection rates of rectal gonorrhoea increased mainly in younger men. To explore this discrepancy we compared trends in STIs and HIV in a cohort of young HIV negative homosexual men from 1984 until 2002.

METHODS

The study population included 863 men enrolled at < or =30 years of age from 1984 onward in the Amsterdam Cohort Studies (ACS). They had attended at least one of the 6 monthly follow up ACS visits at which they completed a questionnaire (including self reported gonorrhoea and syphilis episodes) and were tested for syphilis and HIV. Yearly trends in HIV and STI incidence and risk factors were analysed using Poisson regression.

RESULTS

Mean age at enrollment was 25 years. The median follow up time was 4 years. Until 1995 trends in HIV and STI incidence were concurrent, however since 1995 there was a significant (p<0.05) increase in syphilis (0 to 1.4/100 person years (PY)) and gonorrhoea incidence (1.1 to 6.0/100 PY), but no change in HIV incidence (1.1 and 1.3/100 PY).

CONCLUSIONS

The incidence of syphilis and gonorrhoea has increased among young homosexual men since 1995, while HIV incidence has remained stable. Increasing STI incidence underscores the potential for HIV spread among young homosexual men. However, several years of increasing STIs without HIV, makes the relation between STI incidence and HIV transmission a subject for debate.

An outbreak of hepatitis A among homeless drug users in Rotterdam, The Netherlands

From the end of January to mid-June 2004 (weeks 5-24) a hepatitis A virus (HAV) outbreak occurred among a homeless and drug user community in Rotterdam, The Netherlands. To prevent further spread of the virus within this group and to the general population, the Municipal Health Service of Rotterdam organized a mass vaccination campaign during which 83% (1,515/1,800) of the homeless people were vaccinated. As part of a national HAV typing study, blood and/or fecal samples of 30 Rotterdam HAV IgM+ patients who fell ill during the period of 1 September 2003-1 December 2004 were tested. The tests included RT-PCR and sequencing at the VP3-VP1 and VP1-P2a regions of the HAV genome. It was found that 12 homeless people, one family member of a homeless person and two people without a known risk were infected with a unique subtype 3a strain. Four of the homeless patients became ill after vaccination and were probably infected at the time. This study shows that Dutch homeless people and drug users involved in HAV outbreaks should be offered HAV vaccine actively to prevent further spread of the infection. Furthermore, it was shown by molecular techniques that the unique subtype 3a strain was not found before the Rotterdam outbreak or afterwards, indicating that the mass vaccination campaign was successful.

[Less refusal to participate in HIV screening among pregnant women in the Amsterdam region since the introduction of standard HIV screening using the opting-out method]

In 2003 the Municipal Health Service in Amsterdam started to screen pregnant women for HIV according to the opting-out method. In this method the HIV test is routinely included in the prenatal screening along with hepatitis B virus (HBV) and syphilis. If the woman does not want to be tested for HIV then she must actively opt out of this test. This screening method was chosen because in the universal screening method used in 2002, women had to give their explicit consent to test for HIV and this led to a high refusal rate (13.6%), especially among women from AIDS-endemic countries. After the introduction of the opting-out method, the refusal rate fell from 3% in the first quarter of 2003 to 1.4% in the last quarter of 2003. None of the women refused to be tested for HBV or syphilis. In 2003, the HIV prevalence among pregnant women was 0.3% (35/13.621). The experiences with this screening method in Amsterdam were used to implement the national opting-out method for HIV screening in pregnant women, which was introduced on 1 January 2004.

Performance of routine syphilis serology in the Ethiopian cohort on HIV/AIDS

OBJECTIVES

To assess the performance of routine syphilis screening during 5 year follow up of Ethiopian factory workers, participating in a cohort study on HIV/AIDS.

METHODS

Syphilis serology test results of factory workers, who each donated at least six blood samples were evaluated. Screening in 1997-8 had been performed by the Treponema pallidum particle agglutination (TPPA) assay and in 1999-2001 by the rapid plasma reagin (RPR) test. TPPA had been followed by RPR or RPR by TPPA, in case of a positive screening result. Samples of study subjects showing inconsistent sequential TPPA and/or RPR results were retested independently by three laboratory technicians.

RESULTS

A total of 540 cohort participants (8.3% HIV positive at enrollment) donated 4,376 blood samples (mean 8.3 per subject). From 93 of the 176 participants with at least one positive TPPA result during follow up, 152 samples were retested by RPR and/or TPPA. Based on the revised syphilis test results, the 540 cohort participants were classified as having no (70.5%), past (20.6%), prevalent (6.9%), or incident (2.0%) syphilis. The RPR screening test was difficult to interpret and yielded 8.2% biological false positive (BFP) RPR results, or 3.2% if weak positive results were excluded. There was no correlation between HIV infection and BFP RPR reactions. Sample mix-ups were detected in 1.2%.

CONCLUSION

Evaluation of routine syphilis screening as performed in a long term cohort study on HIV/AIDS in Ethiopia showed difficulties encountered in syphilis screening programmes such as a high percentage of BFP RPR, inconsistencies in interpretation of the RPR test, and sample mix ups. The findings stress the need to develop a syphilis screening assay that is easy to perform and interpret and to implement quality assurance programmes.

[HIV-screening among pregnant women in the region of Amsterdam in 2002]

In 2001, the Municipal Health Service started offering HIV tests to all pregnant women in and around Amsterdam. All midwives and all hospitals but one participated in this HIV screening. In 2002, of the 10,752 pregnant women offered HIV testing 13.6% refused. HIV antibodies were detected in 24 women (0.26%). The HIV prevalence was doubled compared to the prevalence in 1990-1991, but the number of newly HIV-infected pregnant women remained stable (0.1%). The high number of refusals, as a result of which many HIV-infected women might be missed, is alarming. For this reason, in January 2003, the Municipal Health Service started HIV testing by the opting-out approach. Under the opting-out approach, women are notified that an HIV test will be included in the standard test battery, together with tests for hepatitis B and syphilis, unless she explicitly refuses. It is expected that the opting-out approach for HIV screening of pregnant women will be implemented nationwide in 2003.

[HIV-infection and AIDS in the Netherlands: prevalence and incidence, 1987-2001]

OBJECTIVE

To describe the results of HIV-surveillance activities in the Netherlands between 1987 and 2001.

DESIGN

Descriptive.

METHOD

Data were obtained from HIV-surveillance at STI-clinics, laboratory-surveillance in the region Arnhem, surveillance among injecting drug users, the AIDS-notification, STI-registration and the Amsterdam cohort studies on HIV/AIDS.

RESULTS

In the Netherlands, the highest HIV-prevalences were found among injecting drug users (1-26%) and homo- and bisexual men (0-17%). In these high-risk populations, an increase in HIV-prevalence and--incidence, respectively, was found among injecting drug users in Heerlen and homosexual men (> 35 years of age) in Amsterdam. The HIV-prevalence was lower among heterosexuals in the Netherlands (0-2%). However, in certain local populations an increase was seen. In both Amsterdam and Rotterdam, the HIV-prevalence was higher in individuals tested anonymously than in those tested by name.

CONCLUSION

Local increases in HIV-infections have been observed recently, in both high- and medium-risk populations.

Hepatitis B virus transmission from a surgeon to patients during high-risk as well as low-risk procedures: unnoticed transmissions over a 4-year period

Background

Three cases of reported acute hepatitis B virus (HBV) led to the identification of a chronically HBV-infected surgeon, with a high viral load, who was a non-responder after vaccination.

Methods

A retrospective cohort study was conducted on 1564 patients operated on by this surgeon over a 4-year period.

Results

Forty-nine patients (3·1 per cent) were positive for HBV markers. Based on HBV DNA sequencing and epidemiological data, transmission from the surgeon was confirmed in eight, probable in two, possible in 18 and excluded in 21 patients. One case of secondary transmission was identified from a patient to his wife, who died, presumably from fulminant hepatitis. A case–control study identified the duration of operation, the potential risk of the surgical procedure and the occurrence of complications during or after surgery as significant risk factors for HBV infection. At least eight of the 28 patients were infected during low-risk procedures.

Conclusion

Transmission from surgeons to patients at a low rate can remain unnoticed for a long period of time. Prevention requires a more stringent strategy for vaccination and testing of surgeons. It also requires revision of policies allowing HBV-infected surgeons to perform presumed ‘low-risk’ procedures.

[The 14th International Aids Conference: 'Knowledge, commitment and action']

During the world AIDS conference in Barcelona it became clear that the worst-case scenario of 10 years ago has become a reality: the HIV epidemic is continuing to spread. Also in industrialised countries the incidence of HIV infections among homosexual men is once again increasing. An HIV vaccine is still not available. Although the development of antiretroviral therapy continues, HIV inhibitors do not result in an eradication of HIV. It is still not clear as to when therapy can best be started and what the consequences are of temporarily withdrawing therapy. In countries where HIV inhibitors are widely available, the life expectancy of HIV-infected persons is increasing. The life expectancy of HIV patients will possibly decrease again due to an increased resistance towards the currently available antiretroviral drugs.

Low incidence of syphilis among factory workers in Ethiopia: effect of an intervention based on education and counselling

BACKGROUND

The prevalence and incidence of syphilis infection were examined in a cohort study of factory workers in Ethiopia.

METHOD

Between February 1997 and March 1999, 409 men and 348 women were enrolled and followed in the cohort study.

RESULTS

The prevalence (95% CI) of past/current syphilis (positive TPPA serology) was 28.9% (25.7% to 32.3%), and factors associated with past/current syphilis were markers of risky sexual behaviours including HIV infection. In this cohort of factory workers subject to public information/education meetings, testing for HIV antibodies, and individual counselling, the incidence (97.5% one sided CI) of new syphilis infections was 0/691 = 0 (0 to 0.5) per 100 person years.

CONCLUSION

This study has documented a reduction in risky sexual behaviours and a low syphilis incidence among factory workers participating in a cohort study on HIV infection progression in Addis Ababa.

[Syphilis epidemic and an increase of the number of HIV infections among homosexual men attending the Amsterdam venereal disease clinic]

The registered number of cases of early infectious syphilis and of (ano)genital gonorrhoea among the attendees of the outpatient clinic for sexually transmitted diseases of the Amsterdam municipal health service shows a strong increase for both diagnoses in the period 1990-2001, notably in the last few years. Nearly all of this increase is accounted for by homosexual men. Syphilis increased mostly among men aged 35 years and over, gonorrhoea mostly among younger men. The population of older men also showed a distinct increase since 1997 in HIV incidence.

[Post-exposure treatment against HIV outside of the hospital in Amsterdam, January-December 2000]

The Infectious Diseases Department of the Amsterdam Public Health Service regularly sees people who have possibly been exposed to human body fluids infected with hepatitis B virus (HBV), hepatitis C virus (HCV) or human immunodeficiency virus (HIV), as a result of incidents in either a non-hospital-related occupation or during their leisure time. Until January 2000, people reporting possible exposure were referred to hospitals for HIV post-exposure prophylaxis (HIV-PEP), whereas for HBV and HCV, the tracing of the infection source and the follow-up took place at the Public Health Service clinic. Since the introduction of a new protocol in January 2000, the Public Health Service as well as a hospital can establish an indication for HIV-PEP and prescribe it. In 2000, 322 persons reported to the Public Health Service. The source was tested in 194 incidents and an HIV test was carried out on 104 occasions. In 19 cases HIV antibodies were found or the source was known to be HIV positive. A total of 50 people were prescribed HIV-PEP; 16 times after a needle-stick accident, 22 times after a sexual accident, 6 times after a bite-wound and 6 times after direct exposure to human blood. The sources of 30 PEP recipients could be tested and after this 16 recipients could stop with the treatment due to a negative HIV test. In 4 cases PEP treatment was stopped following a review of the indication. Therefore, 30 people had an indication to complete the PEP treatment. Of these, more than 80% reported side effects and 3 people had to withdraw from the treatment at an early stage because of this. The implementation of the protocol has resulted in less confusion because the follow-up now takes place at one location. Compared to other studies, the average time between exposure and treatment is shorter and compliance is good. In the period up to 15 May 2001, no seroconversions had been observed.

[The advances of HIV in the Netherlands: indications but still no definite answers]

Investigations in the province of Limburg demonstrate an increasing HIV prevalence and a high prevalence of injecting and sexual risk behaviour as well as a substantial risk of HIV transmission to the general population. It is recommended that HIV surveillance be directed towards 'bridge populations' such as prostitutes, their customers and immigrants from HIV endemic countries, instead of just drug users. In view of the apparent increase in sexual risk behaviour and sexually transmitted diseases in homosexual men (possibly due to a reduced fear of the disease because of the availability of anti-HIV medication) surveillance should be intensified in that area as well. Only then will it be possible to ascertain whether or not the incidence of HIV in the Netherlands is increasing.

A summary report from Amsterdam: increase in sexually transmitted diseases and risky sexual behaviour among homosexual men in relation to the introduction of new anti-HIV drugs

The worrying increase of sexually transmitted diseases (STDs) in Amsterdam was investigated in two studies carried out by the department of AIDS research of the municipal health service. The results indicate that the introduction of Highly Active Antiretroviral Therapies (HAART) may have had an influence on the increase of STDs and risky sexual behaviours in Amsterdam.

Molecular epidemiology of hepatitis B virus in Amsterdam 1992-1997

To gain insight into the spread of hepatitis B among various risk groups in Amsterdam a 6-year (1992-1997) retrospective DNA sequencing study was carried out on isolates from stored sera from reported primary cases of acute hepatitis B infection. Cases were classified according to risk behavior, as determined in interviews. Of the available serum, a selected region of hepatitis B-virus-DNA was amplified and sequenced. The nucleotide alignments were subjected to phylogenetic tree analysis. When nucleotide alignments were subjected to phylogenetic analysis, the strains of 54 isolates, 26% of the 204 reported primary cases, clustered in five genotypes: A, C, D, E, and F. In genotype A, a cluster related to men having sex with men was identified. In genotype D, two subclusters could be identified: one was related to injecting drug use and another was related to the Moroccan population in Amsterdam. The remaining strains showed a high genetic variability within three different genotypes: F, E, and C. Of the 14 identical isolates in the "homosexual men cluster," one was isolated from a female heterosexual. Of the 14 identical strains in the "drug users strain," six were from non-drug using heterosexual active individuals. In the cluster of twelve isolates related to hepatitis B-endemic areas, probable modes of transmission were varied. Sequence analysis provides important insight into the spread of hepatitis B among various high-risk groups. The analysis indicates that the prevention strategy in The Netherlands fails to stop transmission of hepatitis B from persistently infected individuals originating from hepatitis B endemic countries.

Carrier rate of zidovudine-resistant HIV-1: the impact of failing therapy on transmission of resistant strains

OBJECTIVE

Because maintenance of treatment success in HIV-1 infection requires viruses to remain therapy sensitive in drug-naive seropositive persons, we looked at the primary infections caused by drug-resistant HIV-1 over time. Furthermore, to study the coverage rate of therapy and therapy failure in relation to the transmission of resistant viruses a mathematical model was developed.

DESIGN

The reverse transcriptase and protease genes of viruses were analysed in newly infected people in the period 1990-1998 in the Amsterdam Cohort Study on HIV infection and AIDS in homosexual men.

METHODS

The mathematical model was based on the coverage of drug regimens selecting zidovudine (ZDV) resistance, the lag time in which resistance is gained or lost, the death rate of people infected with resistant virus, and the replacement of resistance-selecting regimens by more potent treatments that substantially reduce viral load and mortality.

RESULTS

Of 43 individuals with a primary HIV-infection, three (7%) harboured ZDV-resistant viruses. The first of the ZDV-resistant strains was transmitted in 1995, the last two in 1996. The build-up of ZDV resistance was described by the mathematical model indicating that the equilibrium level of resistance due to treatment depends only on the treatment rate and the outflow rate of patients with resistance virus.

CONCLUSIONS

Our model indicates that the frequency of viral resistance in a population is determined largely by the number of individuals on insufficient or failing therapy and is influenced only modestly by secondary transmission of ZDV-resistant strains.