Mumps resurgence in a highly vaccinated population: Insights gained from surveillance in Canada, 2002-2020.

Although mumps vaccination has been routine in Canada for decades, mumps cases and outbreaks continue to occur periodically. Mumps surveillance, including monitoring of the mumps virus genotype associated with disease activity, is important to document baseline activity and to advance further research into vaccine effectiveness. Here we describe a detailed analysis of mumps cases that have been detected in Canada from 2002 to 2020, with a focus on the mumps molecular epidemiology. In total, 7395 cases of mumps were reported to the surveillance system, with outbreaks occurring in the years 2007, 2010 and 2016 to 2018. Adolescents and young adults aged 15 to 29 years had the highest risk of being a case (rate ratios ranging from 1.50 to 2.29), compared to adults aged 30 to 39. Genotypes of mumps viruses were determined in 3225 specimens. Genotype G was predominantly detected (96% of genotyped specimens) and was first reported in 2005. Other genotypes were more likely to be detected in cases that also reported travel (or were linked to imported cases) than the cases with genotype G detected (p < 0.0001). The genotype G viruses had little sequence diversity in the 316 nucleotide window used for genotyping (the small hydrophobic protein gene) and mainly belonged to a single phylogenetic lineage that included the MuVi/Sheffield.GBR/1.05 reference sequence. The analysis of over ten years of data has demonstrated that mumps genotype G, specifically belonging to a single lineage, the Sheffield lineage, is the endemically circulating virus in Canada. This lineage is seen also in other countries using the genotype A vaccine. Mumps remains endemic despite high MMR vaccination coverage which has been sufficient to eliminate circulation of measles and rubella in Canada, raising the hypothesis of the evolution towards a vaccine escape mumps virus.

Pertussis epidemiology in Canada, 2005-2019.

Background: Pertussis, also known as whooping cough, is an endemic vaccine-preventable disease that affects the respiratory tract and is caused by the bacterium Bordetella pertussis. Between 1999 and 2004, the adolescent booster dose of pertussis was introduced across Canada. This report describes the epidemiology of pertussis in Canada from 2005 to 2019, the period after adolescent acellular vaccination was recommended. Methods: We analyzed pertussis incidence by year, age groups, sex and geographic region using national surveillance data from the Canadian Notifiable Disease Surveillance System. Hospitalization data from the Discharge Abstract Database was used to investigate pertussis hospitalizations by sex and age. Deaths from pertussis were explored using Statistics Canada's vital statistics data. Vaccination coverage data was gathered from the 2019 Childhood National Immunization Coverage Survey and 2018-2019 Seasonal Influenza Vaccination Coverage Survey. Results: Between 2005 and 2019, there were a total of 33,481 pertussis cases with the average annual incidence rate of 6.4 cases per 100,000 population. The highest average age-specific incidence rate was among infants under one year of age (n=68.7 cases per 100,000 population). There were a total of 1,593 pertussis hospitalizations; nearly 80% of these hospitalizations were infants under one year of age. Hospitalization rates were 8.2 times higher in infants three months or younger compared to infants four to 11 months of age. There were 17 deaths; all among infants under one year of age. Conclusion: The highest morbidity and fatality of pertussis were among infants under one year of age. It is important to take measures to reduce transmission to infants who are too young to be vaccinated. Increasing vaccine coverage in children and pregnant women are important to reduce the burden of disease.

Epidemiology of invasive meningococcal disease in Canada, 2012-2019.

Background: A variety of routine childhood and adolescent meningococcal vaccination programs using monovalent (serogroup C) and quadrivalent (A, C, Y, W) conjugate vaccines have been implemented in Canada since 2002, resulting in a decrease in invasive meningococcal disease (IMD) incidence, particularly in serogroup C. Meningococcal vaccines have also been used for outbreak response, including the multicomponent vaccine serogroup B vaccine. This report describes the epidemiology of IMD in Canada from 2012 to 2019. Methods: Case data were obtained from the National Enhanced IMD Surveillance System between January 1, 2012 and December 31, 2019. Isolates were sent to the National Microbiology Laboratory for confirmation of serogroup and further studies including phenotype and clonal complex identification. Results: A total of 983 cases of IMD were reported between 2012 and 2019. Overall, the age-adjusted incidence of IMD from 2012 to 2019 was 0.34 cases per 100,000 population per year when standardized to the Canadian 2011 population age distribution (95% CI: 0.32-0.36). Infants younger than one year of age had the highest average age-specific incidence rate (3.6 cases per 100,000 population per year, 95% CI: 2.8-4.3). The highest age-adjusted incidence rate was associated with serogroup B (0.17 cases per 100, 000 population per year, 95% CI: 0.16-0.19). Prior to 2015, most invasive serogroup W isolates were identified as clonal complex 22 (ST-22 CC) and the increase in serogroup W in Canada in recent years has been associated with the replacement of the endemic ST-22 CC with the hyper-virulent ST-11 CC. Conclusion: Invasive meningococcal disease is a rare but severe infection in Canada that mostly affects the very young. Serogroup B continues to account for the greatest proportion of disease. Serogroup W associated with ST-11 CC is becoming a growing contributor of disease in all age groups not protected by serogroup W-containing vaccines.

Mumps outbreaks across Canada, 2016 to 2018.

BACKGROUND: An increase in mumps incidence was observed in late 2016 (365 cases in 2016 compared to 59 cases in 2015). This unusual level of mumps activity prompted the Public Health Network Council and the National Advisory Committee on Immunization to request situation awareness updates from the Centre for Immunization and Respiratory Infectious Diseases (CIRID) at the Public Health Agency of Canada in 2017 and 2018. METHODS: A mumps outbreak survey was developed and administered by epidemiologists within CIRID and sent electronically to provincial and territorial public health officials in charge of mumps surveillance. The survey collected information on mumps outbreaks pertaining to demographics, risk factors, laboratory data and public health interventions. The first survey collected data on outbreaks occurring between January 1, 2016 and February 28, 2017, while the second survey contained outbreak data from January 1, 2017 to July 31, 2018. Duplicate outbreaks entries were removed. RESULTS: The response rate for the first and second surveys was 61% and 69%, respectively. Twenty-four mumps outbreaks across nine provinces were reported between January 1, 2016 and July 31, 2018, for a cumulative total of 881 mumps cases. Adolescents and adults 15 to 39 years of age accounted for the majority of cases (80.6%). Specifically, adults 20 to 24 years of age represented the largest proportion of cases (24.6%). Community and social gatherings were the most common exposure setting (62.5%). Slightly more than one third of cases were known to have received at least two doses of mumps-containing vaccine (35.6%). CONCLUSION: Results from the surveys indicate that the increase in mumps activity was widespread throughout Canada, affecting multiple jurisdictions. Young adults accounted for the largest proportion of cases. These surveys provided evidence to support recommendations on the use of additional mumps vaccination in outbreak settings.

Burden of influenza-associated respiratory hospitalizations in the Americas, 2010-2015.

BACKGROUND: Despite having influenza vaccination policies and programs, countries in the Americas underutilize seasonal influenza vaccine, in part because of insufficient evidence about severe influenza burden. We aimed to estimate the annual burden of influenza-associated respiratory hospitalizations in the Americas. METHODS: Thirty-five countries in the Americas with national influenza surveillance were invited to provide monthly laboratory data and hospital discharges for respiratory illness (International Classification of Diseases 10th edition J codes 0-99) during 2010-2015. In three age-strata (<5, 5-64, and ≥65 years), we estimated the influenza-associated hospitalizations rate by multiplying the monthly number of respiratory hospitalizations by the monthly proportion of influenza-positive samples and dividing by the census population. We used random effects meta-analyses to pool age-group specific rates and extrapolated to countries that did not contribute data, using pooled rates stratified by age group and country characteristics found to be associated with rates. RESULTS: Sixteen of 35 countries (46%) contributed primary data to the analyses, representing 79% of the America's population. The average pooled rate of influenza-associated respiratory hospitalization was 90/100,000 population (95% confidence interval 61-132) among children aged <5 years, 21/100,000 population (13-32) among persons aged 5-64 years, and 141/100,000 population (95-211) among persons aged ≥65 years. We estimated the average annual number of influenza-associated respiratory hospitalizations in the Americas to be 772,000 (95% credible interval 716,000-829,000). CONCLUSIONS: Influenza-associated respiratory hospitalizations impose a heavy burden on health systems in the Americas. Countries in the Americas should use this information to justify investments in seasonal influenza vaccination-especially among young children and the elderly.

Burden of influenza, respiratory syncytial virus, and other respiratory viruses and the completeness of respiratory viral identification among respiratory inpatients, Canada, 2003-2014.

BACKGROUND: A regression-based study design has commonly been used to estimate the influenza burden; however, these estimates are not timely and many countries lack sufficient virological data. Alternative approaches that would permit a timelier assessment of the burden, including a sentinel surveillance approach recommended by the World Health Organization (WHO), have been proposed. We aimed to estimate the hospitalization burden attributable to influenza, respiratory syncytial virus (RSV), and other respiratory viruses (ORV) and to assess both the completeness of viral identification among respiratory inpatients in Canada and the implications of adopting other approaches. METHODS: Respiratory inpatient records were extracted from the Canadian Discharge Abstract Database from 2003 to 2014. A regression model was used to estimate excess respiratory hospitalizations attributable to influenza, RSV, and ORV by age group and diagnostic category and compare these estimates with the number with a respiratory viral identification. RESULTS: An estimated 33 (95% CI: 29, 38), 27 (95% CI: 22, 33), and 27 (95% CI: 18, 36) hospitalizations per 100 000 population per year were attributed to influenza, RSV, and ORV, respectively. An influenza virus was identified in an estimated 78% (95% CI: 75, 81) and 17% (95% CI: 15, 21) of respiratory hospitalizations attributed to influenza for children and adults, respectively, and 75% of influenza-attributed hospitalizations had an ARI diagnosis. CONCLUSIONS: Hospitalization rates with respiratory viral identification still underestimate the burden. Approaches based on acute respiratory case definitions will likely underestimate the burden as well, although each proposed method should be compared with regression-based estimates of influenza-attributed burden as a way of assessing their validity.

Leading Indicators and the Evaluation of the Performance of Alerts for Influenza Epidemics.

BACKGROUND: Most evaluations of epidemic thresholds for influenza have been limited to internal criteria of the indicator variable. We aimed to initiate discussion on appropriate methods for evaluation and the value of cross-validation in assessing the performance of a candidate indicator for influenza activity. METHODS: Hospital records of in-patients with a diagnosis of confirmed influenza were extracted from the Canadian Discharge Abstract Database from 2003 to 2011 and aggregated to weekly and regional levels, yielding 7 seasons and 4 regions for evaluation (excluding the 2009 pandemic period). An alert created from the weekly time-series of influenza positive laboratory tests (FluWatch, Public Health Agency of Canada) was evaluated against influenza-confirmed hospitalizations on 5 criteria: lead/lag timing; proportion of influenza hospitalizations covered by the alert period; average length of the influenza alert period; continuity of the alert period and length of the pre-peak alert period. RESULTS: Influenza hospitalizations led laboratory positive tests an average of only 1.6 (95% CI: -1.5, 4.7) days. However, the difference in timing exceeded 1 week and was statistically significant at the significance level of 0.01 in 5 out of 28 regional seasons. An alert based primarily on 5% positivity and 15 positive tests produced an average alert period of 16.6 weeks. After allowing for a reporting delay of 2 weeks, the alert period included 80% of all influenza-confirmed hospitalizations. For 20 out of the 28 (71%) seasons, the first alert would have been signalled at least 3 weeks (in real time) prior to the week with maximum number of influenza hospitalizations. CONCLUSIONS: Virological data collected from laboratories was a good indicator of influenza activity with the resulting alert covering most influenza hospitalizations and providing a reasonable pre-peak warning at the regional level. Though differences in timing were statistically significant, neither time-series consistently led the other.