The first, second and third wave of pandemic influenza A (H1N1)pdm09 in North Denmark Region 2009–2011: a population‐based study of hospitalizations

Abstract

Background and objectivesDenmark experienced three waves of the new pandemic influenza A (H1N1)pdm09 from July 2009 to February 2011. The aim of the study was to describe the epidemiology and clinical characteristics of hospitalized patients in a defined population of North Denmark Region with a mixed urban and rural community of 579 000 inhabitants.MethodsReview of medical records of all hospitalized patients with confirmed influenza A from July 2009 to February 2011.ResultsTwo hundred and seventy‐three patients were admitted to hospital. The age‐related population incidences of hospitalization were as follows: 0–14 years: 111/100 000, 15–64 years: 39/100 000, and ≥65 years: 17/100 000. During the first wave (July 2009–August 2009), three patients were admitted – none received treatment in intensive care units (ICUs), during the second wave (October 2009–January 2010), 158 patients were admitted – nine received treatment in ICUs, and during the third wave (December 2010–February 2011), 112 patients were admitted – 25 received treatment in ICUs. Fourteen patients (5%) died within 30 days of diagnosis (median 55 years; range 14–76 years) and additional seven patients (2·6%) died within 365 days (median 25 years; range 1–86 years).ConclusionsPatients hospitalized with pandemic influenza A (H1N1)pdm09 were predominantly children and younger adults, and only a few patients were >65 years. The third wave was the most severe taking the number and percentage of patients admitted to ICUs and 30‐day mortality into consideration. We observed that the incidence of hospitalizations as well as clinical severity among younger adults did not decline from the second to the third wave.

Population Effects of Influenza A(H1N1) Pandemic among Health Plan Members, San Diego, California, USA, October–December 2009

“…In The Australian and New Zealand Intensive Care (ANZIC) study, from June 1–August 31, 2009, a total of 28.7 cases/1 million inhabitants were admitted to the ICUs of Australia and New Zealand ( 7 ). A population study in Denmark found 9 (5.69%) of 158 patients were admitted to a hospital ICU during the second wave of the 2009 influenza pandemic ( 8 ), compared with ≈7.6% (≈13/171) in this study. …”

Neuraminidase inhibitors for influenza: a systematic review and meta-analysis of regulatory and mortality data

“…83,92 were excluded from the meta-analysis because one was only a synopsis 83 and one compared zanamivir to usual care and not placebo. 92 We finally included 26 zanamivir trials: 14 on treatment in adults, [71][72][73]77,[80][81][82]87,89,91,95,[97][98][99] two in children 78,84 and 10 trials in prophylaxis. 70,79,85,86,88,90,93,94,96,100 Our attempt at collecting sufficient information from regulatory files to reconstruct missing CSRs also failed because the information appeared to be insufficient for a reliable reconstruction.…”

“…In two zanamivir adult trials, 81,82 pneumonia reporting was based on a stricter definition of X-ray confirmation and there was also no significant treatment effect (RR 1.02, 95% CI 0.35 to 3.02; I 2 statistic = 39%). In nine zanamivir trials, 77,79,80,87,89,91,[97][98][99] pneumonia was a self-reported, investigator-mediated, unverified outcome (see Figures 8 and 9). Overall, there was no significant effect of zanamivir on mixed verified and unverified pneumonia in adult treatment (RR 0.90, 95% CI 0.58 to 1.40; I 2 statistic = 0%).…”

Comparison of severely ill patients with influenza A(H1N1)pdm09 infection during the pandemic and post-pandemic periods in Singapore

“…1 shows the temporal distribution of severely ill patients with laboratory confirmed influenza A(H1N1)pdm09 infection admitted to hospitals and the average daily number of attendances for ARI at government primary care clinics from epidemiological week (Eweek) 23 (7)(8)(9)(10)(11)(12)(13) in 2009 to E-week 32 (6)(7)(8)(9)(10)(11)(12) in 2010. In 2009, a steady increase in attendances for ARI was observed from E-week 25 (21)(22)(23)(24)(25)(26)(27) onwards, which peaked in E-week 30 (26 July-1 August), and decreased over the subsequent weeks until E-week 36 (6)(7)(8)(9)(10)(11)(12).…”

“…A study conducted in England reported a greater burden of severe illness with more deaths, more critical care admissions and more hospital admissions due to influenza A(H1N1)pdm09 in the second year of its circulation than in the pandemic year [23]. A population-based study of hospitalisations in Northern Denmark Region also found that in comparison with the pandemic wave, the severity of hospitalised patients and requirement for ICU admission increased in the post-pandemic wave [24]. Similarly, a retrospective cohort study of all patients with laboratory-confirmed influenza A(H1N1)pdm09 infection admitted to a hospital in Heidelberg, Germany, from May 2009 to April 2011 found increased proportion of patients with severe disease and fatal cases in the post-pandemic season [10].…”