ATLANTA, Aug. 24 -- Two new strains of norovirus may be responsible for a nationwide spike in outbreaks late last year that led to 19 deaths, the CDC said.
A 90-year-old woman in North Carolina died of "illness compatible with norovirus infection" and 18 other deaths were associated with outbreaks of acute gastroenteritis, the CDC said in the Aug. 24 issue of Morbidity and Mortality Weekly Report.
The deaths, many of them in long-term nursing facilities, came as the number of reported norovirus outbreaks in 25 states rose from 372 in October through December 2005 to 1,316 in the same period last year, the CDC said.
The agency only gave figures for states in which at least five outbreaks were reported during that period and noted that the numbers are probably an underestimate, because there is no national reporting system for norovirus.
Not all states routinely test for norovirus during outbreaks of gastroenteritis, the CDC said, but the agency's National Calicivirus Laboratory tested 761 stool specimens from 126 outbreaks by reverse transcription-polymerase chain reaction (RT-PCR).
Norovirus was confirmed in 114, of which 87 (76%) were associated with two new GII.4 norovirus variants, dubbed Minerva and Laurens. The two new strains appear to be identical to new strains that appeared in Europe in 2006, the CDC said.
The CDC said it is not clear why the spike in outbreaks occurred. Some possibilities include increased pathogenicity of the new strains, increased transmissibility, and lower immunity in the population.
"The magnitude and consistency of increases in multiple states suggest an actual increase rather than increased reporting," the agency added.
The 90-year-old in North Carolina died in the hospital after three days of loose stools, fever, and dehydration, the agency said, and the primary cause of death was reported as gastroenteritis.
The death came as the state recorded 17 gastroenteritis outbreaks in long-term nursing facilities. All told, 573 residents and 288 staff members were affected, and 36 needed hospital care.
Two deaths in Wisconsin were associated with gastroenteritis outbreaks but a primary cause of death wasn't reported. The deaths came as the state recorded 106 gastroenteritis outbreaks in all of 2006, compared with 23 a year earlier. Tests confirmed that 87 (82%) were caused by norovirus.
From Oct. 1, 2006 through Jan. 31, 2007, 333 gastroenteritis outbreaks were reported in New York, more than four times the 76 reported during the same period a year earlier.
In those outbreaks, 16 people died, although again the primary cause of death was not reported. The state does not routinely test for norovirus, the CDC said, making it difficult to assess the cause of the outbreaks.
Finally, the agency reported, Boston had a spike in gastroenteritis outbreaks from Dec. 1, 2006, through April 1, 2007, with 18 such events, compared with two in the same period a year earlier. Eight were blamed on norovirus after tests.
The CDC noted that good hand hygiene, combined with disinfecting contaminated surfaces, is an effective way of preventing norovirus infections.