Related Experiment Video
Updated: Jun 13, 2026
High-throughput Detection Method for Influenza Virus
Published on: February 4, 2012
Mild form of 2009 H1N1 influenza infection detected by active surveillance: implications for infection control
Ina Jeong1, Chang-hoon Lee, Deog Kyeom Kim
1Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and Lung Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.
Background:
Screening patients with suspected influenza is a key step for infection control within communities and institutions. By analyzing the clinical characteristics of mild 2009 H1N1 influenza cases detected by active surveillance, we assessed the utility of the commonly used influenza case definition.
Methods:
We retrospectively reviewed medical records of 44 patients who were hospitalized and quarantined and who tested positive for the 2009 H1N1 virus using real-time reverse-transcriptase polymerase chain reaction between May 29 and July 28, 2009.
Results:
Patient median age was 17 years (range, 8-79 years), and 37 patients were male (84%). Common symptoms included cough (34/44; 77.3%), subjective fever (23/44; 52.3%), rhinorrhea or nasal congestion (22/44; 50%), sore throat (19/44; 43.2%), and diarrhea (7/44; 15.9%). All patients were treated with oseltamivir after the onset of initial symptoms (mean, 2.6 days). Common laboratory test results included leucopenia (23/44; 52.3%) and mildly elevated C-reactive protein (26/44; 59.1%).
Conclusion:
There were many mild afebrile cases of the 2009 pandemic H1N1 influenza. Cough, mild leukopenia, and mildly elevated C-reactive protein were relatively common clinical manifestations. Thus, case-based surveillance for the index cluster of 2009 pandemic influenza is not an effective method for infection control in communities or hospital settings.
Insights
Mild 2009 H1N1 influenza cases often presented without fever, showing common symptoms like cough and mild leukopenia. Case-based surveillance is ineffective for controlling this pandemic influenza strain in communities and hospitals.
Area of Science:
- Virology
- Infectious Diseases
- Public Health
Background:
- Influenza screening is crucial for infection control in communities and institutions.
- Analyzing mild 2009 H1N1 influenza cases helps evaluate current case definitions.
- Active surveillance aids in understanding influenza transmission dynamics.
Purpose of the Study:
- To assess the utility of the standard influenza case definition.
- To analyze clinical characteristics of mild 2009 H1N1 influenza cases.
- To evaluate the effectiveness of case-based surveillance for pandemic influenza.
Main Methods:
- Retrospective review of medical records for 44 hospitalized patients positive for 2009 H1N1.
- Real-time reverse-transcriptase polymerase chain reaction (RT-PCR) used for confirmation.
- Data collected on symptoms, laboratory results, and treatment.
Main Results:
- Median patient age was 17; 84% were male.
- Common symptoms included cough (77.3%), subjective fever (52.3%), and nasal congestion (50%).
- Leukopenia (52.3%) and elevated C-reactive protein (59.1%) were frequent laboratory findings.
Conclusions:
- Mild, afebrile cases of 2009 pandemic H1N1 influenza were common.
- Cough, mild leukopenia, and elevated C-reactive protein are key clinical indicators.
- Case-based surveillance is not effective for controlling 2009 pandemic influenza.
Related Concept Videos
01:27Influenza
01:28Infectious Diseases and Their Occurrence
01:24Smallpox
01:25Transmission-based Precautions II: Airborne and Protective Environment
Airborne precautions:
Use airborne precautions when treating patients known or suspected to have diseases that spread through the air—for example, tuberculosis or measles. These organisms are present in smaller droplets expelled by an infected person and...