Are comets the cause of epidemics?

Image of the comet Hale-Bopp via WikipediaThe word epidemic won't invoke any great emotion to the modern generations but history has recorded the suffering of millions of people in various parts of the world due to epidemic strike.

Researchers might have pinpointed something or the other that might have caused the eruption of a epidemic disease. But later discoveries have led to various theories that may not always be concurred on the causes.

In 1978, Science Frontier had published a discovery that stated that comets that have entered the earth orbit might have brought with them bacterias and viruses.

To me, it sounds unscientific because viruses and bacterias survive where there is life. Do the discoveries imply that the comets picked up the diseases causing viruses enroute?

"But recent spectroscopic studies of interstellar matter and comets themselves indicate a richness of life-associated compounds that infers that outer space might well be the breeding ground of simple life."-SF dt Jan 1978