Influenza A testing and detection in patients admitted through emergency departments in Sydney during winter 2009: implications for rational testing

Med J Aust. 2010 Oct 18;193(8):455-9. doi: 10.5694/j.1326-5377.2010.tb03999.x.


Aim: To examine factors associated with testing and detection of influenza A in patients admitted to hospital for acute care during the winter 2009 pandemic influenza outbreak.

Design, setting and participants: Retrospective observational study of patients who were tested for influenza A after being admitted to hospital through emergency departments of the Sydney South West Area Health Service from 15 June to 30 August 2009.

Main outcome measures: The association of factors such as age, diagnosis at admission, hospital and week of admission with rates of testing and detection of influenza A.

Results: 17,681 patients were admitted through nine emergency departments; 1344 (7.6%) were tested for influenza A, of whom 356 (26.5%) tested positive for pandemic influenza. Testing rates were highest in 0-4-year-old children, in the peak period of the outbreak, and in patients presenting with a febrile or respiratory illness. Positive influenza test results were common across a range of diagnoses, but occurred most frequently in children aged 10-14 years (64.3%) and in patients with a diagnosis at admission of influenza-like illness (59.1%). Using multivariate logistic regression, patients with a diagnosis at admission of fever or a respiratory illness at admission were most likely to be tested (odds ratios [ORs], 15 [95% CI, 11-21] and 17 [95% CI, 15-19], respectively). These diagnoses were stronger predictors of influenza testing than the peak testing week (Week 4; OR, 7.0 [95% CI, 3.8-13]) or any age group. However, diagnosis at admission and age were significant but weak predictors of a positive test result, and the strongest predictor of a positive test result was the peak epidemic week (Week 3; OR, 120 [95% CI, 27-490]).

Conclusion: The strongest predictor of a clinician's decision to test for influenza was the diagnosis at admission, but the strongest predictor of a positive test was the week of admission. A rational approach to influenza testing for patients who are admitted to hospital for acute care could include active tracking of influenza testing and detection rates, testing patients with a strong indication for antiviral treatment, and admitting only those who test negative to "clean" wards during the peak of an outbreak.

MeSH terms

  • Adolescent
  • Child
  • Child, Preschool
  • Emergency Service, Hospital*
  • Hospitalization*
  • Humans
  • Infant
  • Influenza A virus / classification
  • Influenza, Human / diagnosis*
  • Influenza, Human / epidemiology
  • Influenza, Human / microbiology
  • New South Wales / epidemiology
  • Pandemics*
  • Polymerase Chain Reaction