Heterogeneous risk attitudes and waves of infection.

Many countries have experienced multiple waves of infection during the COVID-19 pandemic. We propose a novel but parsimonious extension of the SIR model, a CSIR model, that can endogenously generate waves. In the model, cautious individuals take appropriate prevention measures against the virus and are not exposed to infection risk. Incautious individuals do not take any measures and are susceptible to the risk of infection. Depending on the size of incautious and susceptible population, some cautious people lower their guard and become incautious-thus susceptible to the virus. When the virus spreads sufficiently, the population reaches "temporary" herd immunity and infection subsides thereafter. Yet, the inflow from the cautious to the susceptible eventually expands the susceptible population and leads to the next wave. We also show that the CSIR model is isomorphic to the SIR model with time-varying parameters.

Takayasu's arteritis associated with Crohn's disease treated with infliximab.

A 23-year-old woman presented with fever, diarrhea, bloody stools, and arthralgia that did not improve despite previous treatments and was diagnosed with Crohn's disease. Remission was achieved after the introduction of infliximab, nutritional therapy, and 5-aminosalicylic acid treatment. However, the patient's blood sedimentation rate remained elevated without symptom recurrence, except for abdominal pain in the following year. Aortic wall thickening in the thoracic descending aorta was also observed on computed tomography. Accumulation in the thoracic descending aorta and abdominal aorta was confirmed using positron emission tomography-computed tomography. The patient was diagnosed with Takayasu's arteritis. The patient's abdominal symptoms resolved, and her blood sedimentation rate normalized after steroid administration.