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Letter
Salmonella
in Denmark
To the Editor: In the large study by Evans and Wegener recently
published in Emerging Infectious Diseases (1), salmonellae
in broiler chickens and pigs significantly decreased after routine in-feed
antimicrobial drug use for growth promotion was terminated in Denmark.
Avoparcin was a frequently used growth promoter in poultry until its ban
in Denmark in 1995 because of its association with the development and
spread of vancomycin-resistant enterococci. On examining Evans and Wegener’s
data, I noticed that a precipitous drop in salmonellae in broiler chickens
appeared to have occurred in early 1996. Do the authors think this drop
was due to the withdrawal of avoparcin? As the authors note, avoparcin
has been associated with increased shedding of salmonellae (including
a dose-response effect) in a number of studies (2,3).
If the large drop (from approximately 25% positive samples in 1995 to
approximately 10% in 1996) is not due to withdrawal of avoparcin, what
do the authors suggest could have caused it?
Do the authors have sufficient numbers of samples to reanalyze their
data in broiler chickens for three periods instead of just two (i.e.,
use the periods January 1995–December 1995, January 1996–December 1997,
and January 1998–December 2000)? This change would take into account the
potential effect of avoparcin withdrawal in 1995.
Also, the most important reason for decreasing food animals’ carriage
of salmonellae is to protect people from becoming ill with Salmonella.
Do the authors have any figures on domestically acquired human infections
with salmonellae in Denmark since early 1995? Is there any temporal association
with the withdrawal of growth promoters?
Peter Collignon*
*Sydney University, Woden, Australia
Suggested citation
for this article:
Collignon P. Salmonella in Denmark (in reply to Evans and Wegener).
Emerg Infect Dis [serial online] 2003 Dec [date cited]. Available
from: URL: http://www.cdc.gov/ncidod/EID/vol9no12/03-0310_03-0570.htm
References
- Evans MC, Wegener HC. Antimicrobial
growth promoters and Salmonella spp., Campylobacter spp.
in poultry and swine, Denmark. Emerg Infect Dis 2003;9:489–92.
- Barrow PA, Smith HW, Tucker JF. The
effect of feeding diets containing avoparcin on the excretion of Salmonella
by chickens experimentally infected with natural sources of Salmonella
organism. J Hyg (Lond) 1984;93:439–44.
- Barrow PA. Further
observations on the effect of feeding diets containing avoparcin on
the excretion of Salmonella by experimentally infected chickens.
Epidemiol Infect 1989;102:239–52.
Back to Top
In Reply: The drop in Salmonella organisms
in broiler chickens becomes evident in September 1995. The ban on avoparcin
occurred in May 1995. These two facts suggest that the first flocks of
broiler chickens produced without avoparcin were slaughtered in August
1995. Thus, the temporal relationship is evident. We have reanalyzed the
data for the three strata January 1994–December 1995, January 1996–December
1997, and January 1998–December 2000. Each stratum is significantly different
from the two others (p < 0.0001).
Arguing in favor of a causal relationship, apart from the temporal relationship,
one would say that no changes in the Salmonella control program
in this period could explain this reduction. Arguing against a causal
relationship, one would say that the levels momentarily bounced back to
nearly the pre-ban level in 1997, despite the avoparcin ban. The subsequent
drop and consistent low level could be explained by changes in the control
program (introduction of serologic Salmonella monitoring in 1997
to 1998). On the basis of our data, drawing a conclusion one or the other
is not possible.
There is a clear temporal association between reduction in Salmonella
in broiler chickens and reduced incidence of domestically acquired Salmonella
infections that can be attributed to domestically produced broilers. This
finding was recently reported in this journal (1).
Mary E. Patrick* and Henrik C. Wegener†
*DeKalb County Board of Health, Decatur, Georgia, USA; and †Danish Veterinary
Institute, Copenhagen, Denmark
Suggested citation
for this article:
Patrick ME, Wegener HC. Salmonella in Denmark (in reply to Collignon).
Emerg Infect Dis [serial online] 2003 Dec [date cited]. Available
from: URL: http://www.cdc.gov/ncidod/EID/vol9no12/03-0310_03-0570.htm
Reference
- Wegener HC, Hald T, Wong DLF, Madsen M, Korsgaard
H, Bager F, et al. Salmonella
control programs in Denmark. Emerg Infect Dis 2003;9:774–80.
Related articles:
http://www.cdc.gov/ncidod/EID/vol9no4/02-0325.htm
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