Louise Pelletier

Risk Factors for Severe Outcomes following 2009 Influenza A (H1N1) Infection: A Global Pooled Analysis

This study analyzes data from 19 countries (from April 2009 to Jan 2010), comprising some 70,000 hospitalized patients with severe H1N1 infection, to reveal risk factors for severe pandemic influenza, which include chronic illness, cardiac disease, chronic respiratory disease, and diabetes.

Risk of severe outcomes among patients admitted to hospital with pandemic (H1N1) influenza

Background: We describe the disease characteristics and outcomes, including risk factors for admission to intensive care unit (ICU) and death, of all patients in Canada admitted to hospital with pandemic (H1N1) influenza during the first five months of the pandemic. Methods: We obtained data for all patients admitted to hospital with laboratory-confirmed pandemic (H1N1) influenza reported to the Public Health Agency of Canada from Apr. 26 to Sept. 26, 2009. We compared inpatients who had nonsevere disease with those who had severe disease, as indicated by admission to ICU or death. Results: A total of 1479 patients were admitted to hospital with confirmed pandemic (H1N1) influenza during the study period. Of these, 1171 (79.2%) did not have a severe outcome, 236 (16.0%) were admitted to ICU and survived, and 72 (4.9%) died. The median age was 23 years for all of the patients, 18 years for those with a nonsevere outcome, 34 years for those admitted to ICU who survived and 51 years for those who died. The risk of a severe outcome was elevated among those who had an underlying medical condition and those 20 years of age and older. A delay of one day in the median time between the onset of symptoms and admission to hospital increased the risk of death by 5.5%. The risk of a severe outcome remained relatively constant over the five-month period. Interpretation: The population-based incidence of admission to hospital with laboratory-confirmed pandemic (H1N1) influenza was low in the first five months of the pandemic in Canada. The risk of a severe outcome was associated with the presence of one or more underlying medical conditions, age of 20 years or more and a delay in hospital admission.

Pandemic influenza in Canadian children: a summary of hospitalized pediatric cases.

A total of 324 pandemic H1N1 cases were reported to the Immunization Monitoring Program, Active from May 1, 2009 to August 31, 2009. As of August 31, 2009, case details were available for 73% (n=235) of these cases. The median age was 4.8 years and 69% of children were older than 2 years of age. In total, 95 (40%) of children were previously healthy. The proportion with an underlying health condition increased with age. Close to 50% of children received antiviral medication. Two children died from the infection. The pediatric risk groups affected and course of disease caused by pandemic H1N1 appear similar to seasonal influenza.

Incidence of hospital admissions and severe outcomes during the first and second waves of pandemic (H1N1) 2009

Background Canada experienced two distinct waves of pandemic (H1N1) influenza during the 2009 pandemic, one in the spring and the second in early fall 2009. We compared the incidence of hospital admissions and severe outcomes (admission to intensive care unit [ICU] and death) during the two waves. Methods We reviewed data on all laboratory-confirmed cases of pandemic (H1N1) influenza that resulted in hospital admission, ICU admission or death reported to the Public Health Agency of Canada by all provinces and territories from Apr. 18, 2009, to Apr. 3, 2010. Results A total of 8678 hospital admissions (including 1473 ICU admissions) and 428 deaths related to pandemic (H1N1) influenza were reported during the pandemic and post-peak period. There were 4.8 times more hospital admissions, 4.0 times more ICU admissions and 4.6 times more deaths in the second pandemic wave than in the first wave. ICU admissions and deaths as a proportion of hospital admissions declined in the second wave; there was a 16% proportional decline in ICU admissions and a 6% proportional decline in deaths compared with the first wave. Compared with patients admitted to hospital in the first wave, those admitted in the second wave were older (median age 30 v. 23 years) and more had underlying conditions (59.7% v. 47.5%). Pregnant women and Aboriginal people accounted for proportionally fewer patients who were admitted to hospital or who died in the second wave than in the first. Interpretation The epidemiologic features of the first and second waves of the 2009 pandemic differed. The second wave was substantially larger and, although the patients admitted to hospital were older and more of them had underlying conditions, a smaller proportion had a severe outcome.

Age-specific Differences in Influenza A Epidemic Curves: Do Children Drive the Spread of Influenza Epidemics?

There is accumulating evidence suggesting that children may drive the spread of influenza epidemics. The objective of this study was to quantify the lead time by age using laboratory-confirmed cases of influenza A for the 1995/1996–2005/2006 seasons from Canadian communities and laboratory-confirmed hospital admissions for the H1N1/2009 pandemic strain. With alignment of the epidemic curves locally before aggregation of cases, slight age-specific differences in the timing of infection became apparent. For seasonal influenza, both the 10–19- and 20–29-year age groups peaked 1 week earlier than other age groups, while during the fall wave of the 2009 pandemic, infections peaked earlier among only the 10–19-year age group. In the H3N2 seasons, infections occurred an average of 3.9 (95% confidence interval: 1.7, 6.1) days earlier in the 20–29-year age group than for youth aged 10–19 years, while during the fall pandemic wave, the 10–19-year age group had a statistically significant lead of 3 days compared with both younger children aged 4–9 years and adults aged 20–29 years (P < 0.0001). This analysis casts doubt on the hypothesis that younger school-age children actually lead influenza epidemic waves.

A benefit-cost analysis of two-dose measles immunization in Canada

In 1992, because of the limitations of the one-dose measles immunization program, the National Advisory Committee on Immunization (NACI) recommended a two-dose measles immunization program to eliminate measles. More recently, NACI recommended also a special catch-up program to prevent predicted measles outbreaks and to achieve an earlier elimination of measles. The objective of this study was to complete a benefit-cost analysis of a two-dose immunization program with and without a mass catch-up compaign compared with the current one-dose program. The resulting benefit: cost ratios vary between 2.61:1 and 4.31:1 depending on the strategy used and the age of the children targeted. Given the parameters established for this analysis, the benefits of a second-dose vaccination program against measles far outweight the costs of such a program under all scenarios.

Modelling the incidence of measles in Canada: An assessment of the options for vaccination policy

A range of vaccination policy options for improving the control of measles in Canada is investigated using a mathematical model to simulate transmission of the disease. Results suggest that a catch up campaign giving a second dose of vaccine to children aged up to 18 years would have an immediate impact on transmission, which could be maintained by the introduction of a routine second dose at either 18 months or 5 years of age. Introducing a routine second dose of vaccine without a catch up campaign would allow continued endemic transmission of measles among older children for at least 10-15 years.

Reduced susceptibility to penicillin among pneumococci causing invasive infection in children - Canada, 1991 to 1998

OBJECTIVE To determine, over time, the rate and serotypes of pneumococci with reduced penicillin susceptibility obtained from children with invasive infection. DESIGN Active, hospital-based, multicentre surveillance spanning from 1991 to 1998. SETTING Eleven Canadian tertiary care paediatric facilities located from coast to coast. POPULATION STUDIED 1847 children with invasive pneumococcal infection whose isolates (from a normally sterile site) were available for serotyping and standardized testing for penicillin susceptibility at the National Centre for Streptococcus. MAIN RESULTS The prevalence of reduced penicillin susceptibility increased from 2.5% of 197 cases in 1991 to 13.0% of 276 cases in 1998. In the latter year, 8.7% of isolates had intermediate level resistance, and 4.3% had high level resistance. Since they were first detected in 1992, strains with high level resistance have been encountered only sporadically at most centres, but by 1998, all centres but two had encountered examples. Of 40 isolates with high level resistance and 101 isolates with intermediate level resistance, serotypes matched those included in new seven-valent conjugate vaccines for children in 97.5% and 79.2% of cases, respectively. CONCLUSIONS Pneumococci with reduced susceptibility to penicillin are increasing in frequency across Canada among children with invasive infection. The Immunization Monitoring Program, Active data indicate that new conjugate vaccines could help to curb infections due to pneumococci with reduced susceptibility to penicillin but are unlikely to control completely the problem of antibiotic resistance.

Immunity to diphtheria in a sample of the Canadian adult population

OBJECTIVE To assess immunity to diphtheria in a sample of Canadian adults. DESIGN A seroprevalence study of a group of plasmapheresis donors was performed over a four-month period in 1996. A convenience sample of 1619 sera was collected to obtain a good distribution by age groups and centres. The determination of diphtheria antitoxin concentrations was performed by neutralization of diphtheria toxin in cell culture. SUBJECTS A total of 1619 plasmapheresis donors from Halifax, Quebec City, London, Calgary and Edmonton were studied. RESULTS Of the 1619 sera, 20.3% tested showed susceptibility to diphtheria (antitoxin concentration less than 0.01 IU/mL). The proportion of susceptibles increased from 9.5% in subjects 30 to 39 years of age to 36.3% in those 60 years of age or more. The age group 20 to 29 years demonstrated a higher proportion of susceptibles (18.3%) than the next age group (30 to 39 years) in four of the five centres. Significant differences in antibody levels were also observed among the centres. There was no statistically significant difference between sexes. CONCLUSIONS Overall, detectable antibody and presumably immunity to diphtheria in the present sample of Canadian adults is relatively good. However, reason(s) for the relatively high proportion of susceptibles in those aged 20 to 29 years of age in certain centres, as well as why Canada has not experienced any diphtheria outbreaks in the past 20 years given these susceptibility levels, should be investigated further.