Systematic review of clinical and epidemiological features of the pandemic influenza A (H1N1) 2009

Abstract

Please cite this paper as: Khandaker et al. (2011) Systematic review of clinical and epidemiological features of the pandemic influenza A (H1N1) 2009. Influenza and Other Respiratory Viruses DOI: 10.1111/j.1750‐2659.2011.00199.x.The aim of this systematic review was to summarise the clinical and epidemiological features of the pandemic influenza A (H1N1) 2009. We did a systematic search of published literature reporting clinical features of laboratory‐confirmed pandemic influenza A (H1N1) 2009 from 1 April 2009 to 31 January 2010. Forty‐four articles met our inclusion criteria for the review. The calculated weighted mean age of confirmed cases was 18·1 years, with the median ranging from 12 to 44 years. Cough (84·9%), fever (84·7%), headache (66·5%), runny nose (60·1%) and muscle pain (58·1%) were the most common symptoms of confirmed cases. One or more pre‐existing chronic medical conditions were found in 18·4% of cases. Almost two‐thirds (64%) of cases were aged between 10 and 29 years, 5·1% were aged over 50 years and only 1·1% were aged over 60 years. The confirmed case fatality ratio was 2·9% (95% CI 0·0–6·7%), an extracted average from 12 of 42 studies reporting fatal cases (937 fatal cases among 31 980 confirmed cases), which gives an overall estimated infected case fatality ratio of 0·02%. Early in the pandemic, disease occurred overwhelmingly in children and younger adults, with cough and fever as the most prevalent clinical symptoms of the confirmed cases. A high infection rate in children and young adults, with sparing of the elderly population, has implications for pandemic influenza management and control policies.

Description of Hospitalized Cases of Influenza A(H1N1)pdm09 Infection on the Basis of the National Hospitalized-Case Surveillance, 2009–2010, Japan

“…CFR in those aged 20 years and older was significantly higher than that in those aged under 20 years. These results were consistent with the results from previous reports and reaffirmed that A(H1N1)pdm09 virus infection led to high morbidity in the young population and a high CFR in the elderly population (4,(7)(8)(9)(10)(11).…”

“…This rate is similar to those found in Mexico, Chile, and Brazil and 50z of the rate observed in Australia, the Unites States, and Argentina during the same period (6,7). Consistent with the results described in other reports, over 80z of hospitalized cases in the present study were young (＜20 years) (4,(7)(8)(9)(10)(11)35). It is interesting to note that the results from several studies have indicated that the elderly were not disproportionately affected by the virus, perhaps because of cross immunity to A(H1N1)pdm09 in this population (12)(13)(14).…”

Efficacy, Safety, and Pharmacokinetics of Intravenous Peramivir in Children with 2009 Pandemic H1N1 Influenza A Virus Infection

“…However, there was no significant difference in clinical efficacy between the young children and older children in the present study (Table 2 and see Table S1 in the supplemental material). The reason why a higher virus titer was observed at baseline in elder children might be that they might have had any disposition that 2009 pandemic viruses tend to grow for unexplained reasons, since a higher incidence of influenza virus infection was reported in elder children and younger adults compared to other age groups during the 2009 -2010 influenza season (17). The median plasma concentration of peramivir was 33,150 ng/ml at the end of the infusion, and it was 20.7 ng/ml between 18 and 24 h after the end of infusion.…”

Risk Factors Associated with Severe Clinical Outcomes of Pandemic H1N1 Infection

“…A meta-analysis of H1N1 pandemic influenza infection showed that the most common symptoms were cough (84.9 %), fever (84.7%), headache (66.5%), runny nose (60.1%) and muscle pain (58.1%) [8].…”