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During the 6 months that COVID-19 has wreaked pandemic havoc on the world's population, much remains to be known about this disease, yet much has already been learned. Now, two studies shed some light on pathophysiology at both extremes of the COVID-19 spectrum.
Investigators in China found that 37 asymptomatic confirmed COVID-19 cases (AC) had a median duration of virus shedding (of unknown infectiousness) that was 5 days longer than that of age- and sex-matched symptomatic persons with COVID-19. AC tested positive for virus-specific IgG and IgM in 81.1% and 62.2% of cases, respectively, compared with 83.8% and 78.4% of symptomatic cases. These differences were maintained during the early convalescent phase (8 weeks after hospital discharge), during which time titers decreased in both groups. Anti- and pro-inflammatory cytokine and chemokine levels were also significantly higher in the symptomatic patients.
Another study used genomewide association analysis to examine 8,582,968 single nucleotide polymorphisms in 1980 patients with COVID-19 in Italy and Spain, looking for genetic factors associated with severe disease, defined as need for supplemental oxygen or ventilator-assisted respiration. Two loci, 3p31.21 and 9q34.2, were associated with susceptibility to and severity of COVID-19; 9q34.2 coincided with the ABO blood group locus. Examination of this locus showed that blood type A had the highest correlation with severe disease, whereas blood group O was associated with reduced risk for severe disease. Homozygosity of the 3p31.21 risk allele was associated with younger age of COVID-19 acquisition.
Long Q-X et al. Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections. Nat Med 2020 Jun 18; [e-pub]. (https://doi.org/10.1038/s41591-020-0965-6)
The Severe Covid-19 GWAS Group. Genomewide association study of severe Covid-19 with respiratory failure. N Engl J Med 2020 Jun 17; [e-pub]. (https://doi.org/10.1056/NEJMoa2020283)
Comment
While these two studies address entirely different aspects of COVID-19 infection, and the study of asymptomatic persons was too small to allow for generalization, they both provide useful prognostic value. The first seems to indicate that, compared with symptomatic patients, asymptomatic patients are potentially able to spread the infection for longer (if infectious) and may also be more susceptible to reinfection. The second illuminates a correlation between blood type and disease severity that may explain the variability of outcomes and might inform therapeutic approaches.