EPIDEMICS FROM THE EYE OF THE PATHOGEN

While a common trend in disease modeling is to develop models of increasing complexity, it was recently pointed out that outbreaks appear remarkably simple when viewed in the incidence vs. cumulative cases (ICC) plane. This article details the theory behind this phenomenon by analyzing the stochastic Susceptible, Infected, Recovered (SIR) model in the cumulative cases domain. We prove that the Markov chain associated with this model reduces, in the ICC plane, to a pure birth chain for the cumulative number of cases, whose limit leads to an independent increments Gaussian process that fluctuates about a deterministic ICC curve. We calculate the associated variance and quantify the additional variability due to estimating incidence over a finite period of time. We also illustrate the universality brought forth by the ICC concept on real-world data for Influenza A and for the COVID-19 outbreak in Arizona. © 2022 SIAM.Published by SIAM.

Severe Activity Of Inflammatory Bowel Disease Is A Risk Factor For Severe Covid-19: Data From The Sicilian Network For Inflammatory Bowel Disease (Sn-Ibd)

Background And Aim: Data From The First Wave Of Covid-19 Pan-Demic Suggested That Patients With Inflammatory Bowel Disease (Ibd) Are Not At Higher Risk Of Being Infected By Sars-Cov-2 Than The General Population And That, In Case Of Covid-19, Treatment With Immunomodulatory Drugs Is Not Associated With Worse Prognosis, With The Possible Exception Of Systemic Steroids. Evidence From The Second Wave Of Covid-19 Pandemic Is Required To Confirm These Findings. Materials And Methods: This Retrospective Observational Study Included Consecutive Ibd Patients Of The Cohort Of The Sicilian Network For Inflammatory Bowel Disease (Sn-Ibd) With Covid-19 Diagnosed By Pcr-Confirmed Presence Of Sars-Cov-2 Genome In A Nasopharyngeal Swab During The Second Covid-19 Pandemic Wave (15th September 2020–15th January 2020). Data Regarding Demo-Graphics, Ibd Features And Treatments, Comorbidities, And Symptoms Of Covid-19 Were Related To Covid-19 Clinical Outcomes. Results: One Hundred Twenty-Two Patients (Mean Age 43.9±16.7 Years;Males 50.0%;Crohn’S Disease 62.3%;Ulcerative Colitis: 37.7%) Were Included (Estimated Cumulative Incidence: 122/10,000 Ibd Patients=0.0122%). Twelve Patients Developed Covid-19-Related Pneumonia (9.8%), 4 (3.3%) Required Respiratory Assistance (Non-Mechanical Ventilation Or Orotracheal Intubation), And 4 Died (Case Fatality Rate: 3.3%). At Multivariate Analysis, Age (Or 1.034, 95% Ci 1.006-1.147, P=0.03) And Severe Ibd Activity (Or 13.465, 95% Ci 1.104-164.182, P=0.04) Were Independent Predictors Of Covid-19-Related Pneumonia, While Severe Ibd Activity (Or 15.359, 95% Ci 1.320-178.677, P=0.03) Was The Only Independent Predictor Of Severe Covid-19, A Composite End-Point Defined As Need For Respira-Tory Assistance And/Or Death. Concomitant Ibd Treatments Were Not Associated With Covid-19 Clinical Outcomes, Even If A Trend Toward A Protective Role Of Tnf-Inhibitors On Pneumonia Development Was Reported (P=0.08). Conclusions: In This Large Cohort Of Patients With Ibd And Covid-19, Severe Ibd Activity Was The Only Risk Factor For Severe Covid-19, While Ibd Treatments Were Not Associated With Worse Outcomes