(Source article for that graph: http://www.cdc.gov/nchs/data/databriefs/db88.htm -- would that they distributed the actual datasets behind the graphs!)
EDIT: URL removed. The link I included appear to be written by an idiot. Sorry.
> A CDC review of mortality patterns in 1993 states: “the decline in life expectancy likely reflects increases in death rates for chronic diseases during the two influenza outbreaks in 1993.” [Morbidity Mortality Weekly 45 (08), 161-64, March 1, 1996] Some increases in chronic disease (diabetes, heart disease, COPD) were “the result of the two influenza epidemics of 1993,” said the report. [Monthly Vital Statistics Report, Volume 44, No. 7(S), page 9, Feb. 29, 1996]
Apologies -- I'd misread the OP to say that it had been the largest jump in 15 years -- meaning the 15 years prior to 1999.
What's interesting here though is that this is not a small signal, precisely because it shows up against the background without any correlation work at all. FTA:
> "We find the largest rise in American mortality rates [in the last 15 years] occurred in 1999, the year Vioxx was introduced, while the largest drop occurred in 2004, the year it was withdrawn," says Unz.