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Clinical and Diagnostic Laboratory Immunology, July 2005, p. 848-854, Vol. 12, No. 7
1071-412X/05/$08.00+0     doi:10.1128/CDLI.12.7.848-854.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Evaluation of Inapparent Nosocomial Severe Acute Respiratory Syndrome Coronavirus Infection in Vietnam by Use of Highly Specific Recombinant Truncated Nucleocapsid Protein-Based Enzyme-Linked Immunosorbent Assay

Fuxun Yu,¹ Mai Quynh Le,² Shingo Inoue,¹ Hong Thi Cam Thai,¹ Futoshi Hasebe,¹ Maria del Carmen Parquet,¹ and Kouichi Morita^1*

Department of Virology, Institute of Tropical Medicine, Nagasaki University, 1-12-4 Sakamoto, Nagasaki 852-8523, Japan,¹ Department of Virology, National Institute of Hygiene and Epidemiology (NIHE), Hanoi, Vietnam²

Received 24 January 2005/ Returned for modification 6 April 2005/ Accepted 18 April 2005

Severe acute respiratory syndrome (SARS) is a recently emerged human disease associated with pneumonia. Inapparent infection with SARS coronavirus (CoV) is not well characterized. To develop a safe, simple, and reliable screening method for SARS diagnosis and epidemiological study, two recombinant SARS-CoV nucleocapsid proteins (N' protein and N₁₂₁ protein) were expressed in Escherichia coli, purified by affinity chromatography, and used as antigens for indirect, immunoglobulin G enzyme-linked immunosorbent assays (ELISA). Serum samples collected from healthy volunteers and SARS patients in Vietnam were used to evaluate the newly developed methods. The N' protein-based ELISA showed a highly nonspecific reaction. The N₁₂₁ protein-based ELISA, with a nonspecific reaction drastically reduced compared to that of the nearly-whole-length N' protein-based ELISA, resulted in higher rates of positive reactions, higher titers, and earlier detection than the SARS-CoV-infected cell lysate-based ELISA. These results indicate that our newly developed SARS-CoV N₁₂₁ protein-based ELISA is not only safe but also a more specific and more sensitive method to diagnose SARS-CoV infection and hence a useful tool for large-scale epidemiological studies. To identify inapparent SARS-CoV infections, serum samples collected from health care workers (HCWs) in Vietnam were screened by the N₁₂₁ protein-based ELISA, and positive samples were confirmed by a virus neutralization test. Four out of 149 HCWs were identified to have inapparent SARS-CoV infection in Vietnam, indicating that subclinical SARS-CoV infection in Vietnam is rare but does exist.

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* Corresponding author. Mailing address: Department of Virology, Institute of Tropical Medicine, Nagasaki University, 1-12-4 Sakamoto, Nagasaki 852-8523, Japan. Phone: 81 95 849 7829. Fax: 81 95 849 7830. E-mail: moritak{at}net.nagasaki-u.ac.jp.

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Clinical and Diagnostic Laboratory Immunology, July 2005, p. 848-854, Vol. 12, No. 7
1071-412X/05/$08.00+0     doi:10.1128/CDLI.12.7.848-854.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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