Infect Chemother.  2010 Apr;42(2):69-75.

Epidemiological and Clinical Characteristics of Pandemic Influenza (H1N1 2009)

• Noh JY
• Yim SY
• Heo JY
• Choi WS
• Song JY
• Cheong HJ
• Kim WJ

Abstract

BACKGROUND
Since early outbreaks in North America in April 2009, the new influenza virus spread rapidly all over the world, and WHO declared a pandemic in June 2009. The objective of this article is to describe the epidemiological and clinical characteristics of patients confirmed with pandemic influenza (H1N1 2009).
MATERIALS AND METHODS
Among all patients confirmed with pandemic influenza (H1N1 2009) in Korea University Guro Hospital from 2 May 2009 to 31 March 2010, we selected 10% of patients aged more than 15 years randomly. Medical records were reviewed retrospectively and clinical findings were analyzed: social history, underlying disease, initial symptoms, and clinical course. Comparative analysis of initial symptoms was performed by time to presentation and age groups: 15-29 years, 30-49 years, 50-59 years, and more than 60 years. In addition, we described fatal cases of pandemic influenza (H1N1 2009).
RESULTS
From 2 May 2009 to 31 March 2010, total number of laboratory-confirmed cases of pandemic influenza (H1N1 2009) was 7,888. The most cases (1,632) developed at epidemic week 46, 2009. The median age of patients was 13 years and more than half of patients (55.4%) were less than 15 years. The median time to presentation was 1 day from onset of symptom. Clinical symptoms were cough (86.9%), sore throat (69.4%), myalgia (63.3%), chill (60.6%), rhinorrhea (57.7%), headache (57.6%), nausea or vomiting (27.4%), and diarrhea (9.3%). Fever was noted more frequently at 15-29 years group than > or =30 years group. Antiviral agent was administered to 274 patients (77.8%): 267 cases with oseltamivir and 7 cases with zanamivir. The median time to administration was 2 days and mean time to defervescence was 3 days. Cough was the most persistent symptom: initial visit (94.1%), on third day (82.4%), and on sixth day (52.9%) by the serial follow up at the same patients. Case fatality rate was 0.05%, and all fatal cases occurred in patients aged > or =50 years.
CONCLUSIONS
Children and adolescents were the most affected group. Clinical symptoms were similar to seasonal influenza. Gastrointestinal symptoms were relatively common, and cough was the most long-lasting symptom.

Keyword

Influenza; Pandemic; H1N1; Epidemiology; Symptom

MeSH Terms

Adolescent
Aged
Child
Cough
Diarrhea
Disease Outbreaks
Fever
Follow-Up Studies
Headache
Humans
Influenza, Human
Korea
Medical Records
Nausea
North America
Orthomyxoviridae
Oseltamivir
Pandemics
Pharyngitis
Retrospective Studies
Seasons
Vomiting
Zanamivir
Oseltamivir
Zanamivir

Figure

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  Figure 1 Epidemiologic curve of laboratory-confirmed cases of pandemic influenza (H1N1 2009) reported in Korea University Guro Hospital from epidemiologic weeks 31, 2009 to 14, 2010 (n=7,888) is presented.

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  Figure 2 Number of laboratory-confirmed cases of pandemic influenza (H1N1 2009) in Korea University Guro Hospital by age and sex from epidemiologic weeks 31, 2009 to 14, 2010 (n=7,888) is shown.

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  Figure 3 This graph shows progress of clinical symptoms of patients with pandemic influenza (H1N1 2009). Cough is a lasting symptom: 52.9% until day 6. Patients complain diarrhea more at day 3 than initial visit (8.8% vs. 17.6%). Data of day 6 include symptoms of day 6±1 of hospital visit.

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