Children, involvement of GI tract and genetics

1. Starting from a very general paper in de “common” press (Bloomberg) pointing at the 5 factors that determine the outcome of a viral infection: inoculum size end virulence, route of infection, host genetics and immune capacity.  Of these, it is presently unknown what the effect is of:  

• Inoculum size: not easy to quantify certainly not in the “infector” nasopharynx;  
• Virulence: limited evidence of importance of “L/S subtypes” but not known whether there are pathologically important “mutational drifts” in the course of this pandemic;
• Route of infection: clearly most pathogenic in the lung, but what is the effect of ocular versus nasal versus buccal infection?  What is the role of the GI tract (see below)?  
• Host genetics: weak beneficial effect of bloodgroup O has been shown and now also of ACE1 polymorphism (see below)
• “Immunity”: is of course a broad notion. It seems that children are best off (although we do not know to what extent -see below), while elderly and/or co-morbid patients do worse.  But remarkable, the few (well-treated) HIV patients that have been described with COVID presented with mild disease.

2.   Children and gastro-intestinal (GI) symptoms:

• A short paper in NEJM described the fate of 171 SARS-CoV-2 positive children in Wuhan from 1371 “assessed”, presumably in the context of contact tracing (?). In any case, 90 % were indeed in a “family cluster”.  Only 27 % were really asymptomatic, but only 3 required intensive care, all with co-existing conditions, of whom 1 died.     
• A more recent review in Paediatrics largely confirms that picture and provides some nice figures (e.g. Fig 3).  The case definitions are also interesting and  it becomes clear that in a proportion of mild to severe cases gastro-intestinal (GI) symptoms may predominate.
• A small study in “Emerging Microbes and Infection” is interesting, because it shows that in at least half of the children (even those who remained asymptomatic) prolonged positive stool samples were found.   
• The evidence of GI involvement is nicely summarized by Wong et al.

3. Genetics; ACE-1 polymorphism: (Delanghe JR et al, U Ghent)

• In an Editorial in Clin Chim Acta, they show that there is an inverse correlation between the prevalence and mortality of COVID-19 in European countries and the frequency of the D allele, which is associated with reduced expression of ACE2.

Best wishes,

Guido