Health workers move a body at the Evandro Freire municipal hospital in Rio de Janeiro. (Silvia Izquierdo/AP)

RIO DE JANEIRO — When the coronavirus first came to Brazil and a call went out for volunteers to work the critical care wards, Isabella Rêllo analyzed the risks. She was 28. She lived alone. She didn't have preexisting conditions.

So while older physicians stepped back from the front lines of the coronavirus response, Rêllo stepped up.