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Letters Section Editor: Robert M. Golub,
MD, Senior Editor.
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.
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 χ2 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), α = .05.
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.
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.
Cheng Y, Cheng G, Chui CH, et al. ABO Blood Group and Susceptibility to Severe Acute Respiratory Syndrome. JAMA. 2005;293(12):1447–1451. doi:10.1001/jama.293.12.1450-c
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