Infect Chemother.  2011 Feb;43(1):36-41. 10.3947/ic.2011.43.1.36.

The Association of Lymphopenia with the Clinical Severity in the Korean Children Admitted to the Hospital with Pandemic (H1N1) 2009 Infection

  • 1Department of Pediatrics, Yonsei University, Wonju College of Medicine, Wonju, Korea.
  • 2Department of Laboratory Medicine, Yonsei University, Wonju College of Medicine, Wonju, Korea.
  • 3Department of Internal Medicine, Yonsei University, Wonju College of Medicine, Wonju, Korea.
  • 4Department of Diagnostic Radiology, Yonsei University, Wonju College of Medicine, Wonju, Korea.


Critical illness due to pandemic (H1N1) 2009 is an emerging threat to global health. In this study, lymphopenia was focused on as a major risk factor for a critical clinical course of pandemic (H1N1) 2009 infection. We investigated the association of lymphopenia at the time of admission with the clinical severity of the admitted children with pandemic (H1N1) 2009 infection. Material and Methods: We performed a retrospective study on the patients who were younger than 15 years of age and who were admitted to Wonju Christian Hospital due to pandemic (H1N1) 2009 infection between August 20, 2009 and February 20, 2010. Pandemic (H1N1) 2009 infection was confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) in all patients. We divided the study period into two periods as August 20 - November 30 2009 (pre-vaccination period) and December 1 2009 - February 20 2010 (post-vaccination period). The clinical differences between two periods were analyzed. To define the role of lymphopenia, we examined the differences of clinical manifestations between the H1N1 patients with lymphopenia and those without lymphopenia.
Among the 2,399 children who had H1N1 infection, 149 patients (6.2%) were admitted under the following diagnoses: pneumonia (67.1%), bronchiolitis/asthma (18.8%), croup (6%) and febrile convulsion (8.7%). The median age of the patients was significantly different between during the pre-vaccination period and the post-vaccination period (6 years of age [range: 0.25-14] vs. 3 years of age, [range: 0.1-14], P<0.05). The proportion of patients who had lymphopenia was significantly different between two periods (39.5% vs. 20%, P<0.05). When we compared the clinical severity between the patients with lymphopenia and those without lymphopenia, age (P<0.0001), the length of hospital stay (P<0.0001) and the serum levels of C-reactive protein (P<0.01) were significantly different.
Our data support that lymphopenia may be a major determining factor that could cause a critical clinical course during pandemic period among children in the Republic of Korea.


H1N1 Influenza A; Pediatrics; Admission; Lymphopenia

MeSH Terms

C-Reactive Protein
Critical Illness
Length of Stay
Republic of Korea
Retrospective Studies
Reverse Transcriptase Polymerase Chain Reaction
Risk Factors
Seizures, Febrile
C-Reactive Protein


  • Figure 1 The differences between the patients with lymphopenia (PL) and the patients without lymphopenia (nonPL) of admitted pandemic (H1N1) 2009 patients according to the age (A), the C-reactive protein (CRP) level (B) and the hospital stay (C). The median age of the PL was significantly older than that of the nonPL (7 years of age vs. 2 years of age, P<0.0001). The median serum level of CRP of the PL was higher than that of the nonPL (5±0.6 mg/dL vs. 1.9±0.4 mg/dL, P<0.0001). The median hospital stay of the PL was longer than that of the nonPL (5.5±0.2 days vs. 4.5±0.2 days, P<0.01). **: P<0.01, ***: P<0.001.

  • Figure 2 The number of patients with hypoxia (oxygen saturation <93% in room air) was significantly higher in the PL than that in the nonPL (P<0.0001). PL, patients with lymphopenia; nonPL, patients without lymphopenia. ***: P<0.001.

Cited by  1 articles

The Influence of Atopic Findings on Severity of Pneumonia in Children with 2009 Pandemic Influenza A (H1N1) Infection
Jong Hee Kim, Hyun Jeong Kim, Im Ju Kang
Korean J Pediatr Infect Dis. 2011;18(2):182-192.    doi: 10.14776/kjpid.2011.18.2.182.


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