Largest measles epidemic in North America in a decade--Quebec, Canada, 2011: contribution of susceptibility, serendipity, and superspreading events.

BACKGROUND: The largest measles epidemic in North America in the last decade, occurred in 2011 in Quebec, Canada, where rates of 1- and 2-dose vaccine coverage among children 3 years of age were 95%-97% and 90%, respectively, with 3%-5% unvaccinated. METHODS: Case patients identified through passive surveillance and outbreak investigation were contacted to determine clinical course, vaccination status, and possible source of infection. RESULTS: There were 21 measles importations and 725 cases. A superspreading event triggered by 1 importation resulted in sustained transmission and 678 cases. The overall incidence was 9.1 per 100,000; the highest incidence was in adolescents 12-17 years old (75.6 per 100,000), who comprised 56% of case patients. Among adolescents, 22% had received 2 vaccine doses. Outbreak investigation showed this proportion to have been an underestimate; active case finding identified 130% more cases among 2-dose recipients. Two-dose recipients had milder illness and a significantly lower risk of hospitalization than those who were unvaccinated or single-dose recipients. CONCLUSIONS: A chance superspreading event revealed an overall level of immunity barely above the elimination threshold when unexpected vulnerability in 2-dose recipients was taken into account. Unvaccinated individuals remain the immunization priority, but a better understanding of susceptibility in 2-dose recipients is needed to define effective interventions if elimination is to be achieved.

No increase in HIV incidence observed in a cohort of men who have sex with other men in Montreal.

To monitor HIV incidence we tested a cohort of men who have sex with men in Montreal for HIV every 6 months. Between 1996 and 2001, 17 out of 1244 participants seroconverted, for an HIV incidence of 0.56 per 100 person-years (py) (95% CL 0.29, 0.83). The incidence decreased over the study period, from 0.75 to 0.34 per 100 py; which was not statistically significant. An in-depth evaluation of the situation in Montreal could identify useful lessons for prevention efforts elsewhere.

Seasonal influenza vaccination uptake in Quebec, Canada, 2 years after the influenza A(H1N1) pandemic.

BACKGROUND: A decrease in seasonal influenza vaccine uptake was observed after the influenza A(H1N1) pandemic in 2009. The goal of our study was to assess seasonal influenza vaccine uptake in 2011-2012, 2 years after the influenza A(H1N1) pandemic mass immunization campaign and to identify the main reasons for having or not having received the vaccine. METHODS: A telephone survey using random-digit dialing methodology was conducted. Case-weights were assigned to adjust for disproportionate sampling and for nonresponse bias. Descriptive statistics were generated for all variables. RESULTS: Seasonal influenza vaccine uptake was 57% among adults aged ≥60 years, 35% among adults with chronic medical conditions, and 44% among health care workers. The main reasons given for having been vaccinated were to be protected from influenza and a high perceived susceptibility to influenza, whereas low perceived susceptibility to influenza and low perceived severity of influenza were the main reasons for not having been vaccinated. CONCLUSIONS: An increase in seasonal influenza vaccine uptake was observed 2 years after the influenza A(H1N1) pandemic. However, vaccine coverage is still below the target level of 80%. More efforts are needed to develop effective strategies to increase seasonal influenza vaccine uptake.

Determinants of HIV seroconversion among men who have sex with men living in a low HIV incidence population in the era of highly active antiretroviral therapies.

OBJECTIVE: To estimate human immunodeficiency virus (HIV) incidence and associated risk factors among men who have sex with men (MSM) participating in the Omega Cohort Study in Montreal, 1996-2003. METHODS: Longitudinal study of 1587 MSM seronegative at baseline with > or =1 six-month follow-up visit. Multivariate Cox regression with time-dependent variables was used for data analysis. RESULTS: HIV incidence was 0.62 per 100 person-years (95% confidence interval: 0.41-0.84). In multivariate analyses compared with subjects not reporting any anal sex with serodiscordant or casual partners, those reporting anal sex with such partners (all P values <0.05), whether consistently protected [hazard ratio (HR) = 3.4], or unprotected exclusively receptive (HR = 12.0), exclusively insertive (HR = 4.7), or both receptive and insertive (HR = 8.3), were at increased risk of seroconversion. Sexual behaviors with seroconcordant regular partners were not associated with seroconversion. CONCLUSION: These results observed in a cohort of MSM with low HIV incidence provide new insights regarding the debate about harm-reduction strategies to prevent sexual HIV transmission.

Nonnegligible increasing temporal trends in unprotected anal intercourse among men who have sexual relations with other men in Montreal.

OBJECTIVE: The objective of this study is to determine temporal trends in unprotected anal intercourse (UAI) among men who have sex with other men (MSM) participating in the Omega Cohort Study, 1997-2003. METHODS: The Omega Cohort Study was a longitudinal study of HIV-negative MSM aged 16 years or older and living in Montreal. Participants completed self-administered questionnaires and interviews every 6 months. Trend analysis using the generalized estimating equation was done for length of cohort membership (visits) and by calendar time for all visits, per type of sexual partner. Odds ratios (ORs) were calculated to measure the odds of increasing UAI per 6-month period. RESULTS: Among subjects who were followed for at least 4 years, UAI increased with regular seroconcordant partners (OR, 1.06, 95% CI 1.04-1.09), and any type of partner (OR, 1.05, 95% CI 1.03- 1.07). There was a nonnegligible increase in UAI with casual partners (OR, 1.05; 95% CI, 1.01-1.09). For the analysis by calendar time, there were increases in UAI between with regular seroconcordant partners (OR, 1.04; 95% CI, 1.02-1.05) and any type of partner (OR, 1.03; 95% CI, 1.02-1.04). There were nonnegligible increases in UAI with casual partners (OR, 1.03; 95% CI, 1.00-1.05) and with any type of partner except regular seroconcordant partner from 15.7% to 18.8% (OR, 1.02; 95% CI, 1.00-1.04). CONCLUSIONS: There was a nonnegligible and consistent increase in UAI among Omega participants, between 1997 and 2003. Continuous trend analysis is important because it allows us to closely follow UAI and to implement intervention strategies that may help to stop or reduce the present trend.

Nonnegligible increasing temporal trends in unprotected anal intercourse among men who have sexual relations with other men in montreal.

OBJECTIVE: To determine temporal trends in unprotected anal intercourse (UAI) among men who have sex with men (MSM) participating in the Omega Cohort Study, 1997 through 2003. METHODS: The Omega Cohort Study was a longitudinal study of HIV-negative MSM aged 16 years or older and living in Montreal. Participants completed self-administered questionnaires and interviews every 6 months. Trend analysis using the generalized estimating equation was done for length of cohort membership (visits) and by calendar time for all visits per type of sexual partner. Odds ratios (ORs) were calculated to measure the odds of increasing UAI per 6-month period. RESULTS: Among subjects who were followed for at least 4 years, UAI increased with regular seroconcordant partners (OR = 1.06, 95% confidence interval [CI]: 1.04 to 1.09) and any type of partner (OR = 1.05, 95% CI: 1.03 to 1.07). There was a nonnegligible increase in UAI with casual partners (OR = 1.05, 95% CI: 1.01 to 1.09). For the analysis by calendar time, there were increases in UAI between regular seroconcordant partners (OR = 1.04, 95% CI: 1.02 to 1.05) and any type of partner (OR = 1.03, 95% CI: 1.02 to 1.04). There were nonnegligible increases in UAI with casual partners (OR = 1.03, 95% CI: 1.00 to 1.05) and with any type of partner except a regular seroconcordant partner from 15.7% to 18.8% (OR = 1.02, 95% CI: 1.00 to 1.04). CONCLUSIONS: There was a nonnegligible and consistent increase in UAI among Omega Cohort Study participants between 1997 and 2003. Continuous trend analysis is important because it allows us to follow UAI closely and to implement intervention strategies that may help to stop or reduce the present trend.

Lack of evidence of sexual transmission of hepatitis C virus in a prospective cohort study of men who have sex with men.

OBJECTIVES: We studied the prevalence and incidence of hepatitis C virus (HCV) infection in the ongoing Omega Cohort Study of men who have sex with men (MSM). METHODS: From January to September 2001, consenting men (n = 1085) attending a follow-up visit to the ongoing Omega Cohort Study were tested for HCV. If the test results were positive for HCV, we compared them with test results from previous serum samples collected from the time of entry into the original cohort study to determine the time of infection. RESULTS: HCV prevalence at entry was 2.9% and was strongly associated with injection drug use (32.9% vs 0.3%, P<.0001). Only 1 seroconversion was identified in 2653 person-years of follow-up (incidence rate = 0.038 per 100 person-years). The seroconverter was an active injection drug user who reported needle sharing. CONCLUSIONS: Sexual transmission of HCV among MSM appears to be rare.