Jane Whelan

Mumps outbreak among vaccinated university students associated with a large party, The Netherlands, 2010

We investigated a mumps outbreak within a highly vaccinated university student population in the Netherlands by conducting a retrospective cohort study among members of university societies in Delft, Leiden and Utrecht. We used an online questionnaire asking for demographic information, potential behavioural risk factors for mumps and the occurrence of mumps. Vaccine status from the national vaccination register was used. Overall, 989 students participated (20% response rate). Registered vaccination status was available for 776 individuals, of whom 760 (98%) had been vaccinated at least once and 729 (94%) at least twice. The mumps attack rate (AR) was 13.2% (95%CI 11.1-15.5%). Attending a large student party, being unvaccinated and living with more than 15 housemates were independently associated with mumps ((RR 42 (95%CI 10.1-172.4); 3.1 (95%CI 1.7-5.6) and 1.8 (95%CI 1.1-3.1), respectively). The adjusted VE estimate for two doses of MMR was 68% (95%CI 41-82%). We did not identify additional risk factors for mumps among party attendees. The most likely cause of this outbreak was intense social mixing during the party and the dense communal living environment of the students. High coverage of MMR vaccination in childhood did not prevent an outbreak of mumps in this student population.

Mumps vaccine effectiveness against orchitis.

To the Editor: Yung et al. reported in the April 2011 issue of Emerging Infectious Diseases on the epidemiologic characteristics of the nationwide mumps outbreak in England and Wales in 2004−2005 (1). The associated effect of disease was considerable, with >43,000 reported cases and >2,600 hospitalizations. Compared with the prevaccine era, the average age of infection was higher, with infection occurring mostly in older teenagers and young adults (2). Older age at infection is associated with a higher risk of certain complications, particularly orchitis (3). Yung et al. reported that among cases of mumps, previous mumps measles rubella (MMR) vaccination offered considerable protection against orchitis, meningitis, and hospitalization (1).

Targeted vaccination programme successful in reducing acute hepatitis B in men having sex with men in Amsterdam, The Netherlands

BACKGROUND & AIMS In the Netherlands, transmission of hepatitis B virus occurs mainly within behavioural high-risk groups, such as in men who have sex with men. Therefore, a vaccination programme has targeted these high-risk groups. This study evaluates the impact of the vaccination programme targeting Amsterdams large population of men who have sex with men from 1998 through 2011. METHODS We used Amsterdam data from the national database of the vaccination programme for high-risk groups (January 1, 1998 to December 31, 2011). Programme and vaccination coverage were estimated with population statistics. Incidence of acute hepatitis B was analyzed with notification data from the Amsterdam Public Health Service (1992-2011). Mathematical modelling accounting for vaccination data and trends in sexual risk behaviour was used to explore the impact of the programme. RESULTS At the end of 2011, programme coverage was estimated at 41% and vaccination coverage from 30% to 38%. Most participants (67%) were recruited from the outpatient department for sexually transmitted infections and outreach locations such as saunas and gay bars. Incidence of acute hepatitis B dropped sharply after 2005. The mathematical model in which those who engage most in high-risk sex are vaccinated, best explained the decline in incidence. CONCLUSIONS Transmission of hepatitis B virus among Amsterdams men who have sex with men has decreased, despite ongoing high-risk sexual behaviour. Vaccination programmes targeting men who have sex with men do not require full coverage; they may be effective when those who engage most in high-risk sex are reached.

Q fever among culling workers, the Netherlands, 2009-2010.

In 2009, dairy goat farms in the Netherlands were implicated in >2,300 cases of Q fever; in response, 51,820 small ruminants were culled. Among 517 culling workers, despite use of personal protective equipment, 17.5% seroconverted for antibodies to Coxiella burnetii. Vaccination of culling workers could be considered.

Incidence of acute hepatitis B in different ethnic groups in a low-endemic country, 1992–2009: Increased risk in second generation migrants

BACKGROUND The Netherlands is a low-incidence country for acute hepatitis B (HBV) infection (1.2/100,000 in 2010), where it is typically acquired in adulthood through injecting drug use or homosexual exposure. Recently, the number of heterosexually acquired acute infections in the Netherlands has increased. Ethnicity may be a risk factor. We describe trends in the incidence of acute HBV among heterosexual adults in ethnic groups in Amsterdam from 1992 to 2009 and discuss future control of HBV in the Netherlands. METHODS We studied all cases of acute HBV acquired in heterosexuals aged ≥15 years in the Amsterdam region (1992-2009, n=238) by ethnic group. Incidence rates were estimated as the average number of cases per 100,000 per year. Using Poisson regression, we calculated univariable and multivariable incidence rate ratios (IRR) by ethnic group over calendar year, by age and gender. RESULTS The incidence in first generation migrants from HBV-endemic countries (FGM) was 4.1/100,000 showing no trend over time. Since 1999, incidence in Dutch-born cases in Amsterdam has increased by 13% annually from 0.2/100,000 in 1999 to 2.1/100,000 in 2009 (annual IRR 1.13, 95% CI:1.0-1.22). From 2004 to 2009, the incidence in native Dutch/Western in Amsterdam was 1.6/100,000 (reference for IRR), in FGM was 4.3/100,000 (IRR of 2.7, 95% CI:1.8-4.2) and in Dutch-born second generation migrants (SGM) was 3.7/100,000 (IRR:2.4, 95% CI:1.2-4.7). CONCLUSION Incidence of acute hepatitis B in Amsterdam in FGM and SGM is higher than in the native Dutch population. Low-endemic countries with migrant populations from HBV-endemic areas should consider offering screening and vaccination to both FGM and SGM.

Unprotected casual sex equally common with local and Western partners among long-term Dutch travelers to (sub)tropical countries.

We studied casual sexual partnerships and consistency of condom use among Dutch long-term, travelers to (sub)tropical regions. Forty-two percent of casual sexual partnerships (n = 192/462) were with local partners, of which 39% were unprotected. Fewer travelers to Sub-Saharan Africa had casual sex, but partners ethnicity was not significant in predicting condom use.

Evaluation of hepatitis a vaccine in post-exposure prophylaxis, the Netherlands, 2004-2012

Background The secondary attack rate of hepatitis A virus (HAV) among contacts of cases is up to 50%. Historically, contacts were offered immunoglobulin (IG, a human derived blood product) as post-exposure prophylaxis (PEP). Amid safety concerns about IG, HAV vaccine is increasingly recommended instead. Public health authorities’ recommendations differ, particularly for healthy contacts ≥40 years old, where vaccine efficacy data is limited. We evaluated routine use of HAV vaccine as an alternative to immunoglobulin in PEP, in those considered at low risk of severe infection in the Netherlands. Methods Household contacts of acute HAV cases notified in Amsterdam (2004-2012) were invited ≤14 days post-exposure, for baseline anti-HAV testing and PEP according to national guidelines: immunoglobulin if at risk of severe infection, or hepatitis A vaccine if healthy and at low risk (aged <30, or, 30-50 years and vaccinated <8 days post-exposure). Incidence of laboratory confirmed secondary infection in susceptible contacts was assessed 4-8 weeks post-exposure. In a vaccinated subgroup, relative risk (RR) of secondary infection with estimated using Poisson regression. Results Of 547 contacts identified, 191 were susceptible to HAV. Per-protocol, 167 (87%) were vaccinated (mean:6.7 days post-exposure, standard deviation(sd)=3.3) and 24 (13%) were given immunoglobulin (mean:9.7 days post-exposure, sd=2.8). At follow-up testing, 8/112 (7%) had a laboratory confirmed infection of whom 7 were symptomatic. All secondary infections occurred in vaccinated contacts, and half were >40 years of age. In healthy contacts vaccinated per-protocol ≤8 days post-exposure, RRref. ≤15 years of secondary infection in those >40 years was 12.0 (95%CI:1.3-106.7). Conclusions Timely administration of HAV vaccine in PEP was feasible and the secondary attack rate was low in those <40 years. Internationally, upper age-limits for post-exposure vaccination vary. Pending larger studies, immunoglobulin should be considered PEP of choice in people >40 years of age and those vulnerable to severe disease.

Immunogenicity of a hexavalent vaccine co-administered with 7-valent pneumococcal conjugate vaccine. Findings from the National Immunisation Programme in The Netherlands.

The hexavalent vaccine Infanrix hexa was introduced into the national childhood vaccination schedule in the Netherlands in 2006. It is offered, concomitantly with pneumococcal vaccine (Prevenar), to children at increased risk of hepatitis B, administered in a 4-dose schedule at 2, 3, 4 and 11 months of age. We assessed the immunogenicity of the HBV component of Infanrix hexa co-administered with Prevenar, and compared pertussis and Hib components in Infanrix hexa with the standard Infanrix-IPV+Hib vaccine. Target thresholds for immune responses were achieved for all antigens studied. Over 99% (163/164) of children vaccinated with Infanrix hexa achieved an adequate immune response (³10 mIU/ml) to the HBV component and peak anti-HBs geometric mean concentration (GMC) was 2264mIU/ml (95%CI:1850-2771mIU/ml). The GMC of a pertussis component, filamentous hemagglutinin (FHA), of Infanrix-hexa was significantly lower in children vaccinated with Infanrix hexa and Prevenar than in children vaccinated with Infanrix-IPV+Hib. Universal infant HBV vaccination using Infanrix hexa was introduced in the Netherlands in 2011. Despite very high rates of seroconversion for the HBV component of Infanrix hexa, its long term immunogenicity and effectiveness should be monitored after concomitant vaccination.

Ecologic Study of Meningococcal B Vaccine and Neisseria gonorrhoeae Infection, Norway.

To the Editor: Gonorrhea is a sexually transmitted disease that can cause pelvic inflammatory disease, ectopic pregnancy, and salpingitis in women and infertility in men and women. Rates vary; incidence is 12.5 cases/100,000 population in Europe (1) and ≈6,000 cases/100,000 population in parts of sub-Saharan Africa (2). Recurrent infection is common, antimicrobial drug resistance is growing, and no licensed vaccine is available to protect against gonorrhea infection. Components of some meningococcal B (MenB) vaccines could provide protection against the causative bacterium, Neisseria gonorrhoeae (M. Pizza, pers. comm.), because the meningococcus bacterium is of the same Neisseria genus and the 2 bacteria share key protein antigens, such as the outer membrane vesicle (OMV). Ecologic evidence from Cuba supports a decline in gonococcus infection after a nationwide OMV vaccine campaign in the 1980s (3). In Norway, a trial of another OMV MenB vaccine (MenBvac, Norwegian Institute of Public Health, Oslo, Norway) was conducted among teenagers during 1988–1992. We retrospectively examined associations between MenB vaccine coverage during 1988–1992 and national gonorrhea rates for persons >16 years of age during 1993–2008 in Norway.

Risk factors for secondary transmission of Shigella infection within households: implications for current prevention policy

BackgroundInternationally, guidelines to prevent secondary transmission of Shigella infection vary widely. Cases, their contacts with diarrhoea, and those in certain occupational groups are frequently excluded from work, school, or daycare. In the Netherlands, all contacts attending pre-school (age 0–3) and junior classes in primary school (age 4–5), irrespective of symptoms, are also excluded pending microbiological clearance. We identified risk factors for secondary Shigella infection (SSI) within households and evaluated infection control policy in this regard.MethodsThis retrospective cohort study of households where a laboratory confirmed Shigella case was reported in Amsterdam (2002–2009) included all households at high risk for SSI (i.e. any household member under 16 years). Cases were classified as primary, co-primary or SSIs. Using univariable and multivariable binomial regression with clustered robust standard errors to account for household clustering, we examined case and contact factors (Shigella serotype, ethnicity, age, sex, household size, symptoms) associated with SSI in contacts within households.ResultsSSI occurred in 25/ 337 contacts (7.4%): 20% were asymptomatic, 68% were female, and median age was 14 years (IQR: 4–38). In a multivariable model adjusted for case and household factors, only diarrhoea in contacts was associated with SSI (IRR 8.0, 95% CI:2.7-23.8). In a second model, factors predictive of SSI in contacts were the age of case (0–3 years (IRRcase≥6 years:2.5, 95% CI:1.1-5.5) and 4–5 years (IRRcase≥6 years:2.2, 95% CI:1.1-4.3)) and household size (>6 persons (IRR2-4 persons 3.4, 95% CI:1.2-9.5)).ConclusionsTo identify symptomatic and asymptomatic SSI, faecal screening should be targeted at all household contacts of preschool cases (0–3 years) and cases attending junior class in primary school (4–5 years) and any household contact with diarrhoea. If screening was limited to these groups, only one asymptomatic adult carrier would have been missed, and potential exclusion of 70 asymptomatic contacts <6 years old from school or daycare, who were contacts of cases of all ages, could have been avoided.