Evaluation of the completeness of reporting of invasive meningococcal disease

Challenges to the surveillance of meningococcal disease in an era of declining incidence in montréal, Québec

OBJECTIVES

Though rare in Montréal, meningococcal disease continues to cause serious morbidity and mortality. In an era of declining incidence, our objective was to evaluate the sensitivity and the timeliness of case reporting and the capacity to statistically detect disease clusters.

METHODS

We used the public health department's reportable disease database (RDD) to calculate the timeliness of reporting by physicians and laboratories for the period 1995 to 2008. The sensitivity of case reporting was evaluated through capture-recapture estimation using the RDD and the hospitalization discharge database (MED-ECHO). To evaluate the detection of cases clustered by time and proximity, we applied scan statistics to the RDD with cases coded by time and geographic location for the period 1992 to 2008.

RESULTS

While the system sensitivity was judged to be high at 94%, physicians reported only 54% of cases. A total of 92.3% of cases were notified by physicians or laboratories within seven days, meaning that in theory, 13 cases were not notified in time to conduct thorough contact tracing and offer chemoprophylaxis to close contacts. In high-incidence years, scan statistics detected two statistically-significant clusters one to two weeks earlier than traditional detection through the manual monitoring of cumulative cases.

CONCLUSIONS

To improve system performance, we recommended increasing the emphasis of laboratory reporting, reinforcing early reporting by physicians and if incidence increases, using scan statistics to identify clusters that can add to a public health practitioner's initial "hunch" of an emerging outbreak.

Cases of malaria, hepatitis A, and typhoid fever among VFRs, Quebec (Canada)

BACKGROUND

Visiting friends and relatives (VFRs), especially young VFRs, are increasingly recognized in the industrialized world as a high-risk group of travelers.

METHODS

We performed a descriptive, cross-sectional design study of cases of malaria, hepatitis A, and typhoid reported to the Quebec registry of notifiable diseases between January 2004 and December 2007, occurring in VFRs and non-VFRs travelers.

RESULTS

VFRs account for 52.9% of malaria cases, 56.9% of hepatitis A cases, and 94.4% of typhoid cases reported in Quebec travelers. Almost all (91.6%) of the malaria cases among VFRs were acquired in Africa, particularly in sub-Saharan Africa. An important proportion of malaria cases among VFRs (86.4%) were due to Plasmodium falciparum. The vast majority (76.6%) of typhoid fever cases among VFRs were reported by travelers who had visited the Indian subcontinent. Among VFRs, 40% of total cases were under 20 y of age, compared to less than 6% among non-VFRs. Those under 20 years of age also accounted for 16.9% of malaria cases, 50% of typhoid cases, and 65.2% of hepatitis A cases among VFRs.

CONCLUSION

Our study clearly shows that VFR children should be a primary target group for pre-travel preventive measures.

Effectiveness of serogroup C meningococcal conjugate vaccine: a 7-year follow-up in Quebec, Canada

BACKGROUND

A mass immunization campaign was implemented in 2001 to control a serogroup C meningococcal disease outbreak, and a newly licensed serogroup C meningococcal conjugate vaccine (C-MCV) was used. In 2002, 1 C-MCV dose was routinely offered to children 12 months of age.

OBJECTIVE

To assess the epidemiologic effect of the campaign and C-MCV effectiveness during a 7-year period according to age at vaccination and delay since vaccine administration.

METHODS

Cases of invasive meningococcal infection reported to public health authorities and the reference laboratory during the period 1990 to 2008 were obtained to calculate year- and age-specific incidence rates. Multiple sources were used to ascertain the immunization status of cases. Immunization registry data were used to estimate age-specific C-MCV uptake rates in different birth cohorts. Vaccine effectiveness was estimated by Mantel-Haenszel method and logistic regression models.

RESULTS

After mass immunization campaign, meningococcal C disease incidence decreased markedly not only in highly vaccinated but also in poorly vaccinated and nonvaccinated birth cohorts. Overall vaccine effectiveness was 87.4% (95% CI: 75.4%-94.2%) with lower protection in children vaccinated <2 years of age and waning of protection of higher magnitude in this age group.

CONCLUSION

Results support the current Canadian recommendation to provide booster vaccination for adolescents.

A secure protocol for protecting the identity of providers when disclosing data for disease surveillance

BACKGROUND

Providers have been reluctant to disclose patient data for public-health purposes. Even if patient privacy is ensured, the desire to protect provider confidentiality has been an important driver of this reluctance.

METHODS

Six requirements for a surveillance protocol were defined that satisfy the confidentiality needs of providers and ensure utility to public health. The authors developed a secure multi-party computation protocol using the Paillier cryptosystem to allow the disclosure of stratified case counts and denominators to meet these requirements. The authors evaluated the protocol in a simulated environment on its computation performance and ability to detect disease outbreak clusters.

RESULTS

Theoretical and empirical assessments demonstrate that all requirements are met by the protocol. A system implementing the protocol scales linearly in terms of computation time as the number of providers is increased. The absolute time to perform the computations was 12.5 s for data from 3000 practices. This is acceptable performance, given that the reporting would normally be done at 24 h intervals. The accuracy of detection disease outbreak cluster was unchanged compared with a non-secure distributed surveillance protocol, with an F-score higher than 0.92 for outbreaks involving 500 or more cases.

CONCLUSION

The protocol and associated software provide a practical method for providers to disclose patient data for sentinel, syndromic or other indicator-based surveillance while protecting patient privacy and the identity of individual providers.

Vaccinating adolescents against meningococcal disease in Canada: a cost-effectiveness analysis

BACKGROUND

One dose of serogroup C meningococcal conjugate vaccine (MCV-C) at 12 months of age is the most common immunization schedule in Canada, but immunity may wane over time.

OBJECTIVES

To assess the cost-effectiveness of a booster dose at 12 years of age with either MCV-C or a quadrivalent ACYW135 meningococcal conjugate vaccine (MCV-4).

METHODS

A simulation model for assessing both the direct and indirect effects of vaccination was developed. Age- and serogroup-specific incidence and fatality rates were derived from Canadian surveillance data. Vaccine efficacy was estimated from data from the U.K. and Spain, assuming an age-dependent decline of vaccine efficacy over time. Expected vaccine coverage rates were 90% at 12 months, and 70% at 12 years. Herd immunity was modeled using UK data. Vaccine purchase price per dose was $23 for MCV-C and $70 for MCV-4. Costs and health outcomes were discounted at 3% per year. Results, expressed in 2004 Canadian $ and from a societal perspective, were presented for a steady state situation and a population of 1 million.

RESULTS

Under the "no vaccination" base scenario, 5.7 cases of vaccine-preventable meningococcal disease would occur each year. Vaccination at 12 months using MCV-C would reduce the burden of disease by 32%. Adding MCV-C at 12 years of age would reduce the number of cases by 55% at no marginal cost, while using MCV-4 would result in a disease reduction of 78% for a marginal cost of $31000 per QALY gained. Comparing MCV-4 with MCV-C as a booster dose, the incremental cost-effectiveness ratio would be $113000 per QALY. The efficacy of C-MCV vaccination at 12 months and the differential price between the two vaccines were the parameters having the strongest impact on the cost/QALY ratios. Any increase in the incidence of serogroup Y will improve the marginal cost-effectiveness ratio associated with MCV-4.

CONCLUSION

Adolescent revaccination would be beneficial. Using C-MCV would be the most cost-effective option, while using MCV-4 would be more effective but would also require more investment.

[Public health: the control of meningococcal disease in Quebec]

A first outbreak of serogroup C meningococcal disease occurred in the province of Quebec in 1990-1992 and lead to a mass immunization campaign using polysaccharide vaccines. In 2001, a second outbreak was identified and a mass vaccination campaign was carried out, using the newly licensed conjugate vaccine. Clinical, epidemiological, economic and social studies were instrumental in the decision making for implementing these control programs.

The effectiveness of serogroup C meningococcal vaccine estimated from routine surveillance data

Serogroup C meningococcal vaccine effectiveness was estimated from routine surveillance data, based on a comparison of the proportion of vaccine and non-vaccine serogroups in vaccinated and unvaccinated reported cases. Between 1 April 1993 and 31 March 1998, 109 eligible cases were reported. Among the 54 cases caused by serogroup C, 38 had been vaccinated. Among the 55 cases caused by non-vaccine serogroups, 49 had been vaccinated. Vaccine effectiveness was estimated at 71% (95% CI: 21-89%), a value similar to that obtained in the same population by a cohort study. Effectiveness was lower in children immunized before the age of 10. This demonstrates that meningococcal vaccine effectiveness can be estimated from information obtained routinely from cases only, as an alternative to the more expensive cohort or case-control designs.