From January to November 2006, 223 norovirus outbreaks
were reported in Hungary. For 128 out of 223 outbreaks (57%) the norovirus
agent was laboratory confirmed (72 by ELISA, 56 by PCR). Norovirus was thought
to be the probable cause for the remaining 95 outbreaks on the basis of clinical
and epidemiological data.
Since summer 2006, the majority of outbreaks in Hungary have been caused
by the new variant of the virus GGII.4 2006b, which was identified early
this year in several European countries, including Hungary (in April). A
rise in norovirus circulation had been expected in subsequent seasons following
the appearance of this new variant.
In the second quarter of 2006, an especially high virus circulation was
noted in north east Hungary. This was was thought to be due to the outbreak
of drinking water-related diseases which occurred in June 2006 in Miskolc
(the capital of Borsod-Abaúj-Zemplén county in the north east), affecting
3600 people. Although the outbreak had multiple causes, the predominant
agent was found to be norovirus. Following this outbreak, the number of
norovirus outbreaks in the area increased. In the third quarter of 2006,
increased norovirus activity spread to the neighbouring county of Heves
and to central part of Hungary, and in October and November 2000 it reached
the northern lowlands and the northern and western Trans-danubian region.
So far, in 2006, norovirus outbreaks have been reported as occurring in
similar settings to outbreaks in recent years: 42% (54 outbreaks) took place
in hospitals, 31% (39 outbreaks) in residential homes for old people, 13%
(16 outbreaks) in settings with children (such as nurseries and schools)
and the remaining 15% (19 outbreaks) in other places. In most outbreaks,
including the recent ones in November 2006, the transmission was person
to person; other modes of transmission played a negligible role.
Compared with previous years, the overall number of norovirus outbreaks
reported in Hungary between January and November 2006 is almost 2.5 times
higher than during the same period in 2005, and exceeds the median value
for the years 2002-2004.
In the first quarter of both 2005 and 2006, a similar number of outbreaks
was reported (62 and 68 respectively). However, in the second quarter of
2006, the number of outbreaks almost doubled when compared with the same
period of 2005, and in the third quarter and October and November of 2006,
it was four times higher than in the same period of 2005. (Figure 1)
The total number of probable and laboratory confirmed norovirus outbreaks
in Hungary in 2005 did not exceed the median value for 2000-2004 (consequently,
2005 was considered to be a year with low norovirus activity), whereas from
January to November 2006 the number of outbreaks in all periods was above
the median of these previous years, and in October and November 2006 it
was three times higher than the median (Figure 1).
Figure 1. Total number of probable and confirmed norovirus outbreaks,
Hungary, January 2005 - November 2006.
Norovirus surveillance in Hungary began in 1998, and since 2002, Hungarian
national authorities have participated in the ‘Food-borne Viruses in Europe’
After the routine bacteriological investigation of an outbreak has been
completed, representative samples undergo ELISA analysis and both positive
and negative samples are sent to the national reference laboratory for gastroenteric
viruses for further investigation, where a PCR test and comparative genetic
analysis of the viruses identified are performed .
Thanks to this procedure, norovirus has been established as the cause
of 569 gastroenteritis outbreaks in Hungary since 1998. In a further 583
outbreaks, the norovirus was thought to be the probable cause on the basis
of clinical and epidemiological data alone, because laboratory investigation
either was not performed or yielded negative results (Figure 2).
Figure 2. Gastroenteric outbreaks caused by norovirus or non-bacterial
unknown agent 1998 - 2006
According to the surveillance data gathered so far, 2002/2003 has been
the most active norovirus season since surveillance began. The sharp rise
in number of norovirus outbreaks in that period was due to the increased
circulation of the then newly-identified variant (G II.4 2002) which was
detected in Europe in 2002, including in Hungary . The increase in the
number of outbreaks seen in 2006 seems to follow a similar pattern and be
due to the newly identified genotype GII.4 2006 variants, but as the 2006/2007
season is not yet over, it will be possible to draw the final conclusions
only after the surveillance data has been completed and put in a larger