Pneumonia occurs in all climates and seasons ; incidence is highest in winter and spring in temperate zones. Resistance is generally high, but may be lowered by exposure to a cold and wet environment indicating infectious causative agent is a psychrophilic. Psychrophiles grow best within the range 20 degree centigrade, many continuing to grow at temperatures down to 0 centigrade.
As found out by John Leslie of Edinburgh in the nineteenth century ; a body radiates most energy when its surface is dull black and least when its surface is highly polished. In application of this : The bright surface reduces the heat lost in winter, and keeps the interior cool in summer. We ourselves choose light-colored clothing in summer for the same reason, and in very hot countries white clothing is generally the rule.
In view of above, I normally see Pope Francis donning or in white vestments most of time. Has this exposed him chronically to lower temperatures conducive niche for double pneumonia he have contracted?