According to the book "Sunderland Corporation Transport - A History of Public Service" in 1921 the trams were carrying 32,500,000 passengers a year, so lots of opportunities to catch some kind of infection from a passenger. Certainly my great grandfather who was acting Station Master at Sunderland Railway Station in 1883 seemed to be unlucky. He died at 32 of confluent smallpox. Avril Steward