Predictors of clinical outcome in a national hospitalised cohort across both waves of the influenza A/H1N1 pandemic 2009–2010 in the UK

Abstract

BackgroundAlthough generally mild, the 2009–2010 influenza A/H1N1 pandemic caused two major surges in hospital admissions in the UK. The characteristics of patients admitted during successive waves are described.MethodsData were systematically obtained on 1520 patients admitted to 75 UK hospitals between May 2009 and January 2010. Multivariable analyses identified factors predictive of severe outcome.ResultsPatients aged 5–54 years were over-represented compared with winter seasonal admissions for acute respiratory infection, as were non-white ethnic groups (first wave only). In the second wave patients were less likely to be school age than in the first wave, but their condition was more likely to be severe on presentation to hospital and they were more likely to have delayed admission. Overall, 45% had comorbid conditions, 16.5% required high dependency (level 2) or critical (level 3) care and 5.3% died. As in 1918–1919, the likelihood of severe outcome by age followed a W-shaped distribution. Pre-admission antiviral drug use decreased from 13.3% to 10% between the first and second waves (p=0.048), while antibiotic prescribing increased from 13.6% to 21.6% (p<0.001). Independent predictors of severe outcome were age 55–64 years, chronic lung disease (non-asthma, non-chronic obstructive pulmonary disease), neurological disease, recorded obesity, delayed admission (≥5 days after illness onset), pneumonia, C-reactive protein ≥100 mg/litre, and the need for supplemental oxygen or intravenous fluid replacement on admission.ConclusionsThere were demographic, ethnic and clinical differences between patients admitted with pandemic H1N1 infection and those hospitalised during seasonal influenza activity. Despite national policies favouring use of antiviral drugs, few patients received these before admission and many were given antibiotics.

Mitogenic stimulation accelerates influenza-induced mortality by increasing susceptibility of alveolar type II cells to infection

“…Although individual risk for mortality is low, a significant subset of infected patients develop pneumonia, the most lethal consequence of influenza (5). Those at the highest risk for infection and complications include pregnant women (6), the elderly (>65 y) (7), the very young (<5 y of age, and especially less than 2 y), smokers (8), those exposed to inhaled toxicants such as oxygen (9) and air pollutants (10), and patients with chronic illnesses such as diabetes and emphysema (11,12). Increased risk is often ascribed to impairment of the immune system, and differential susceptibility of the airway epithelium is seldom considered in mechanistic studies of host factors that predispose to IAV infection and poor outcomes.…”

Study of the Epidemiological Features and Clinical Manifestations of the Preceding Epidemic of Influenza A (H1N1) as a Guide for Dealing With the 2015 Outbreak in the Qazvin Province, Iran

“…In a study on the pediatric age group, asthma and neurologic impairment were the most prevalent underlying risk factors (22). Regarding the role of obesity and being overweight, there are established evidences concerning the place of high BMI in severity of disease (19,23,24). In our study, BMI was shown to be an independent risk factor of Hypoxemia in the course of the 2009 pandemic influenza A (H1N1).…”

Differences between asthmatics and nonasthmatics hospitalised with influenza A infection

“…While influenza A infection, including the H1N1 2009 pandemic, is associated with greater morbidity and mortality among patients with asthma as compared to the general population [7,8], among those hospitalised for pandemic influenza, the presence of asthma has been associated with less severe outcomes [9]. This is in contradistinction to obesity, for example, which is associated with an important increase in severe outcomes, including death [9].…”