CHICAGO — A 5-year-old boy who fell ill in a city-run migrant shelter in December died of sepsis and a bacterial infection, according to the Cook County medical examiner’s office. Jean Carlos Martinez Rivero, died Dec. 17 of sepsis and streptococcus pyogenes, a bacterial infection that can cause strep throat, pathologists at the medical examiner’s office concluded in a report issued late this week. Coronavirus, adenovirus and rhinovirus infections were listed as secondary causes of death. Mayor Brandon Johnson on Saturday expressed condolences to Jean Carlos’ family in a statement that also de…