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Yoo, Noh, Yoo, Shin, Choi, Kim, Chey, Kim, Kim, Lee, Kuak, and Shin: Outbreak of Swine-Origin Influenza A (H1N1); Experience of a Regional Center in Seoul during a Month, August-September 2009
Original Article

Korean J Clin Microbiol 2010;13(3):103-108.

Published online: 21 September 2010

DOI: https://doi.org/10.5145/KJCM.2010.13.3.103

Outbreak of Swine-Origin Influenza A (H1N1); Experience of a Regional Center in Seoul during a Month, August-September 2009

Soo Jin Yoo1, Choong-Hee Noh2, 3, Hyeon Mi Yoo2, Won Chang Shin4, Soo Jeon Choi4, Baek-Nam Kim4, Myoung-Jae Chey5, Chang Keun Kim5, Kyunam Kim6, Sang-Lae Lee7, Eun-Young Kuak1, Bo-Moon Shin1, 2

1Department of Laboratory Medicine, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea

2Department of Infection Control Office, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea

3Department of Urology, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea

4Department of Internal Medicine, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea

5Department of Pediatrics, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea

6Department of Family Medicine, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea

7Department of Emergency Medicine, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea

Correspondence: Bo-Moon Shin, Department of Laboratory Medicine, Sanggye Paik Hospital, Inje University College of Medicine, 761-1 Sanggye 7-dong, Nowon-gu, Seoul 139-707, Korea. (Tel) 82-2-950-1227, (Fax) 82-2-950-1244; (E-mail) bmshin@unitel.co.kr

Received 4 May 2010       Revised 28 June 2010       Accepted 20 July 2010

Copyright © 2010 Korean Journal of Clinical Microbiology

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

The aim of this study is to clarify the epidemiology of swine-origin influenza A (H1N1) virus 2009 (S-OIV) during the first month of outbreak at one of influenza clinic in Seoul, Korea.

Methods

We documented the epidemiologic and clinical features of S-OIV-confirmed cases who visited a university hospital in Northeastern Seoul between August 21 and September 20, 2009. Nasopharyngeal swab of patients with acute febrile respiratory illnesses were evaluated with rapid influenza antigen tests and multiplex RT-PCR for S-OIV and seasonal influenza A.

Results

A total of 5,322 patients with acute febrile respiratory illnesses were identified at our influenza clinic for the study period. S-OIV was confirmed in 309 patients by RT-PCR. The patients ranged from 2 months to 61 years of age and 189 patients (61.2%) were teenagers. Eighty-one patients had known contact with S-OIV-confirmed patients in schools (N=61), households (N=15), and healthcare facilities (N=3). Frequent symptoms were fever (94.5%), cough (73.1%), sore throat (52.1%), and rhinorrhea (50.5%). Gastrointestinal symptoms were also present in 10 patients (4.9%). Ten patients (4.9%) required hospitalizations. Seventy patients (22.7%) could not take oseltamivir at the first visits, however, all of them recovered without complication. Rapid antigen tests showed the sensitivity of 44.4% (130/294). Patients with positive antigen tests, compared with negative antigen tests, showed higher frequencies of rhinorrhea (60.8% vs 43.3%, P=0.004) and stuffy nose (33.8% vs 20.1%, P=0.012).

Conclusion

S-OIV infections spread predominately in school-aged children during the early accelerating phase of the outbreak. Rapid influenza antigen tests were correlated with nasal discharge and obstruction.

Keywords: Influenza A virus, Swine-origin influenza, H1N1

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Fig. 1.
Daily numbers of patients who visited the influenza clinic due to acute febrile respiratory illnessess (N=5,322), patients with PCR-confirmed S-OIV (N=309), and patients with PCR or rapid influenza A antigen positive results (N=491), August to September 2009. Abrupt increase of the visits to the influenza clinic was observed at the end of August, and it followed by the increase of S-OIV patients.
kjcm-13-103f1.tif
Table 1.
Demographic and clinical features of 309 patients with confirmed swine-origin influenza A (H1N1) virus
Characteristics Value
  No./total No. (%)
Male 199/309 (64.4%)
Age  
 Median 15 years
 Range 3 months to 61 years
 Age group No./total No. (%)
  0∼4 years 17/309 (5.5)
  5∼9 years 51/309 (16.5)
  10∼14 years 57/309 (18.4)
  15∼19 years 132/309 (42.7)
  20∼29 years 34/309 (11.0)
  30∼39 years 9/309 (2.9)
 40∼49 years 1/309 (0.3)
  ≥50 years 8/309 (2.6)
Underlying isorder No./total No. (%)
 Absent 287/296 (97.0)
 Congestive heart failure 4/296 (1.3)
 Asthma 3/296 (1.0)
 Chronic renal failure 2/296 (0.6)
Intervals from onset of symptom to visit No./available No. (%)
 ≤24 hours 44/281 (15.7)
 24∼48 hours 119/281 (42.3)
 48∼72 hours 70/281 (22.7)
 72∼96 hours 33/281 (10.7)
 ≥96 hours 15/281 (5.3)
Sources of S-OIV infection No./total No. (%)
 School 61/304 (20.1)
 Household 15/304 (4.9)
 Healthcare 3/304 (1.0)
 Workplace 2/304 (0.7)
 Outside Korea 5/304 (1.6)
 Sporadic 218/304 (70.9)
Clinical symptoms No./total No. (%)
 Fever 292/295 (97.3)
 Cough 226/295 (76.6)
 Sore throat 161/295 (54.6)
 Rhinorrhea 156/295 (52.9)
 Stuffy nose 79/295 (26.8)
 Headache 22/295 (7.5)
 Myalgia 10/295 (3.4)
 Diarrhea 6/295 (2.0)
 Nausea 4/295 (1.4)
 Abdominal pain 3/295 (1.0)
Table 2.
Frequencies of each clinical symptom according to rapid influenza A antigen test results in 204 patients with confirmed swine-origin influenza A (H1N1) patients
  Antigen (＋) patients (N=130) Antigen (−) patients (N=164) P value
    (N=164)  
Fever, N (%) 128 (96.9%) 154 (93.9%) 0.260
Cough, N (%) 93 (71.5%) 123 (75.0%) 0.588
Sore throat, N (%) 71 (54.6%) 84 (51.2%) 0.644
Rhinorrhea, N (%) 79 (60.8%) 71 (43.3%) 0.004
Stuffy nose, N (%) 44 (33.8%) 33 (20.1%) 0.012
Table 3.
Positive rates of rapid influenza A antigen test according to age and symptom interval in 204 patients with confirmed swine-origin influenza A (H1N1) patients
  No. of patients (N=294) No. of antigen (＋) patients (N=130) % of antigen (+) patients
Age
 0∼4 years 17 9 52.9%
 5∼9 years 48 19 39.6%
 10∼19 years 185 81 43.8%
 ≥20 years 44 21 47.7%
Interval from onset
 ≤24 hours 44 11 25.0%
 24∼48 hours 119 53 44.5%
 48∼72 hours 69 40 58.0%
 ≥72 hours 46 23 51.1%
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