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ABO Blood Group and Susceptibility to Severe Acute Respiratory Syndrome
To the Editor: ABO blood group has been reported to influence susceptibility to the Norwalk virus and Helicobacter pylori infections.1-2 The prevalence of H pylori infection in Taiwan is significantly higher in patients with blood group O than in those with other blood groups,3 possibly due to a reduced number of H pylori receptors in persons with group A or group B blood. We studied the relationship between ABO blood group and the development of severe acute respiratory syndrome coronavirus (SARS-CoV) infection in a group of health care workers who were exposed to an index SARS patient and who were not wearing any personal protective equipment.
Methods
The first major SARS outbreak in Hong Kong occurred in March 2003. The index case was a patient who was admitted to Prince of Wales Hospital, a 1000-bed general hospital.4 The patient had been placed in an open ward with 20 other patients because the outbreak had not been recognized. The staff did not use any personal protective equipment during that period. We studied all physicians, nurses, medical students, and allied health staff who had worked at least one 4-hour shift in that ward during the 8 days between the patient’s admission and recognition of the outbreak. Visitors to the ward were excluded from the study. SARS was confirmed in the staff by presence of SARS-CoV IgG antibody using SARS-CoV–infected Vero cells fluorescent assay.5 ABO and Lewis phenotypes were determined using DiaMed gel card (DiaMed AG, Cressier sur Morat, Switzerland). The study was approved by the institutional review board of the Department of Medicine and Therapeutics, Chinese University of Hong Kong. Oral informed consent was obtained from all participants.
Categorical data were analyzed using the 2-tailed  2 or Fisher exact test with SPSS for Windows version 11.0 (SPSS Inc, Chicago, Ill). Based on the sample size, we had 90% power to detect at least a 90% increase or decrease in odds ratio (OR),  = .05.
Results
Forty-five staff fulfilled the inclusion criteria. ABO distributions were similar to that reported for the local population6: O (42.2%), A (17.8%), B (33.3%), and AB (6.7%). All participants were Le(a – b+) and therefore ABH secretors. Thirty-four exposed participants had serologically confirmed SARS-CoV infection with symptom onset within 10 days of exposure to the index case. Eleven exposed participants remained seronegative after 2 months. Group O participants were less likely to become infected when compared with non-O participants (OR, 0.18; 95% confidence interval, 0.04-0.81) (Table). An increased likelihood in group B participants was present (OR, 1.46) but not statistically significant.
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Table. Odds of SARS-CoV Infection According to Blood Groups
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Comment
There appears to be an association between ABO blood type and the likelihood of SARS infection after exposure. Our study closely resembled a challenge model because all participants had worked in the vicinity of a single index case without wearing protective equipment. Because SARS is a fatal disease, it would not be ethical to do a true human challenge model as was done in the Norwalk virus study.2
Persons with type O phenotype have been reported to be more susceptible to the Norwalk virus, and saliva from group O secretors binds more efficiently to Norwalk virus–like particles.2 Group O secretors had a relative risk of 1.56 for Norwalk virus infection compared with other ABO blood groups. The H pylori blood group antigen binding adhesin (BabA) mediates binding of H pylori to the fucosylated Le(b) histo-blood group antigen present on the surface of gastric epithelial cells, resulting in increased risk of gastric disease.1 The prevalence of H pylori infection is twice as high in group O participants compared with other ABO groups. In contrast, we found that blood group O was associated with reduced susceptibility to SARS infection. It is possible that the SARS-CoV, like H pylori, may have variable binding affinity to differing ABH substances present on gut epithelial cells. A difference in binding could affect viral entry and susceptibility to SARS infection.
There are important limitations to consider in interpreting this study. There was likely unequal exposure to the index patient among the participants; we could not quantify this. The small sample size limits our power to detect less than a 90% increase or decrease in risk. However, investigating exposure to additional patients after the index outbreak would be difficult because of the effects of different SARS-CoV strains and the use of personal protective gear. These results should be considered very preliminary, but suggest that factors related to ABO blood type may be related to susceptibility to SARS. If these results can be replicated, further research should focus on the mechanism of this effect; understanding this could lead to development of prophylactic and therapeutic strategies for this fatal disease, as well as risk stratification in infection control.
Yufeng Cheng, MD, PhD;
Gregory Cheng, MD, PhD;
C. H. Chui, PhD;
F. Y. Lau, PhD
Department of Medicine & Therapeutics
Paul K. S. Chan, MBBS, MSc, MRCPath, FHKCPath
Department of Microbiology
Margaret H. L. Ng, MBChB, MRCPath
Department of Anatomical & Cellular Pathology
Joseph J. Y. Sung, MD, PhD
Department of Medicine & Therapeutics
Raymond S. M. Wong, MBChB, MRCP
raymondwong{at}cuhk.edu.hk
Department of Medicine & Therapeutics
Chinese University of Hong Kong
Hong Kong, China
1. Boren T, Falk P, Roth KA, Larson G, Normark S. Attachment of Helicobacter pylori to human gastric epithelium mediated by blood group antigens. Science. 1993;262:1892-1895.
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2. Lindesmith L, Moe C, Marionneau S, et al. Human susceptibility and resistance to Norwalk virus infection. Nat Med. 2003;9:548-553.
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3. Lin CW, Chang YS, Wu SC, Cheng KS. Helicobacter pylori in gastric biopsies of Taiwanese patients with gastroduodenal diseases. Jpn J Med Sci Biol. 1998;51:13-23.
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4. Lee N, Hui D, Wu A, et al. A major outbreak of severe acute respiratory syndrome in Hong Kong. N Engl J Med. 2003;348:1986-1994.
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5. Chan PK, Ip M, Ng KC, et al. Severe acute respiratory syndrome–associated coronavirus infection. Emerg Infect Dis. 2004;10:530-532.
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6. Mak KH, Cheng S, Yuen C, Chua E, Lin CK, Leong S. Survey of blood group distribution among Chinese blood donors in Hong Kong: an update. Vox Sang. 1994;67:50.
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Letters Section Editor: Robert M. Golub, MD, Senior Editor.
JAMA. 2005;293:1450-1451.
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