Staphylococcus aureus are relatively common bacteria which can inhabit humans without adverse effects. (Wikipedia is here.) However, if they penetrate the skin, these bugs are the cause of many ailments, from minor skin infections to blood infections and pneumonia. A staph strain called the 80/81 staph phage caused widespread infections in repeated outbreaks in the 1950s and 60s. This pandemic was brought under control using synthetic pennicilin analogues; and other staph strains became the predominant sources of infection.
But 80/81 did not disappear. In last week's issue The Lancet, scientists report that a recently characterized clone of staph infections (of the diagnostic category CA-MRSA, for community acquired methicillin resistant S. aureus), appears to be a direct descendant of the 80/81 strain. This variant is quite nasty, associated with skin boils and abcesses even in young and healthy people; and it retains several toxins from the ancestral strain. Right now the 80/81 related isolates can still be treated with a second class of antibiotic, the vancomycins; but other staph strains have become resistant to these as well. This new-old infectious agent could develop into a major public health challenge.
UPDATE: The Washington Post ran an article on April 6 which appears to refer to the same staph isolate (no name is offered). Scary stuff