Sero-Prevalence and Incidence of A/H1N1 2009 Influenza Infection in Scotland in Winter 2009–2010

Abstract

BackgroundSero-prevalence is a valuable indicator of prevalence and incidence of A/H1N1 2009 infection. However, raw sero-prevalence data must be corrected for background levels of cross-reactivity (i.e. imperfect test specificity) and the effects of immunisation programmes.Methods and FindingsWe obtained serum samples from a representative sample of 1563 adults resident in Scotland between late October 2009 and April 2010. Based on a microneutralisation assay, we estimate that 44% (95% confidence intervals (CIs): 40–47%) of the adult population of Scotland were sero-positive for A/H1N1 2009 influenza by 1 March 2010. Correcting for background cross-reactivity and for recorded vaccination rates by time and age group, we estimated that 34% (27–42%) were naturally infected with A/H1N1 2009 by 1 March 2010. The central estimate increases to >40% if we allow for imperfect test sensitivity. Over half of these infections are estimated to have occurred during the study period and the incidence of infection in late October 2009 was estimated at 4.3 new infections per 1000 people per day (1.2 to 7.2), falling close to zero by April 2010. The central estimate increases to over 5.0 per 1000 if we allow for imperfect test specificity. The rate of infection was higher for younger adults than older adults. Raw sero-prevalences were significantly higher in more deprived areas (likelihood ratio trend statistic = 4.92,1 df, P = 0.03) but there was no evidence of any difference in vaccination rates.ConclusionsWe estimate that almost half the adult population of Scotland were sero-positive for A/H1N1 2009 influenza by early 2010 and that the majority of these individuals (except in the oldest age classes) sero-converted as a result of natural infection with A/H1N1 2009. Public health planning should consider the possibility of higher rates of infection with A/H1N1 2009 influenza in more deprived areas.

The Impact of Birthweight on Adult Minor Illness: A Study on a Sub-Clinical Population

“…Many public health policies and interventions focus upon combating major health issues. However, whilst not as serious as major communicable and non-communicable diseases, minor illnesses are common to the human condition [2][3][4][5] . They add to the burden of morbidity and for those who are economically active minor illness reduces their effectiveness or removes them temporarily from the workforce 1 .…”

“…During the 2009 A/H1N1flu pandemic, telephone interviews in ten states of America indicated that 13.5% of under 18s and 4.7% over 18's had flu like symptoms 3 . Based on a microneutralisation assay, McLeish et al, 4 estimate that 44% of the adult population of Scotland were sero-positive for A/H1N1 influenza by 1 March 2010 with the majority of these being a result of natural infections as opposed to vaccine. Further, Baguelin et al, 5 report that during this same period, 52% of 5 -14 year olds in England had confirmed infections, which was up to 40 times higher than estimated from clinical surveillance.…”

Origin and fate of A/H1N1 influenza in Scotland during 2009

“…We have previously shown using highly specific diagnostic assays that the virus had infected approximately 20 % of the adult population of Scotland by 1 December 2010 (McLeish et al , 2011). From the same study, it is possible to estimate a clinical attack rate of approximately 10 % for this virus, rendering classical epidemiological contact tracing almost impossible.…”

“…The school-holiday period is taken as the end of the summer phase of the pandemic (Health Protection Agency, 2010). Cases began to increase again in August and September, more rapidly in eastern Scotland, and the winter phase in Scotland peaked in late November 2009 (Health Protection Scotland, 2011; McLeish et al , 2011). …”

Lessons from Ebola: Improving infectious disease surveillance to inform outbreak management

“…Importantly, it would also cover ethical requirements. Ethical considerations both delayed and limited surveillance in the UK during the 2009 H1N1 influenza A pandemic (45) and can be difficult to deal with rapidly even during a major emergency, as recent experience with trials for ebolavirus vaccines illustrates.…”