Published Date: 2006-12-02 00:00:00
Subject: PRO/AH/EDR> Salmonellosis, serotype Norfolk, tomatoes - USA (Multistate)
Archive Number: 20061202.3409
SALMONELLOSIS, SEROTYPE NORFOLK, TOMATOES - USA (MULTISTATE)
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Fri, 1 Dec 2006
From: Brent Barrett <email@example.com>
Source: CIDRAP [edited]
Officials are investigating a 2nd outbreak of salmonellosis linked to
restaurant tomatoes that occurred over the summer and early fall of
2006, sickening 106 people in 19 states.
The outbreak, first reported 28 Nov 2006 in the Produce News,
involves restaurant tomatoes contaminated with _Salmonella enterica_
serotype Norfolk. The organism typically causes fever and nonbloody
diarrhea that resolves in a week.
In early Nov 2006, the CDC confirmed that an outbreak of _Salmonella
enterica_ serotype Typhimurium, which sickened 183 Americans in 21
states, plus 2 Canadians, was linked to restaurant tomatoes.
Christine Olson, MD, MPH, an epidemiology intelligence service
officer with the enteric diseases epidemiology branch of the CDC,
told CIDRAP News that the outbreak was detected by PulseNet, an
electronic network for sharing molecular fingerprinting (pulsed-field
gel electrophoresis) data. She said the outbreak began in Jun 2006
and appears to have ended in Oct 2006. She said the bulk of cases
occurred in Aug and Sep 2006; 15 cases were reported in Oct 2006.
A case-control study the CDC launched in response to the _S._ Norfolk
outbreak revealed that about 35 to 40 percent of patients were
hospitalized, she said. Most of the _S._ Norfolk cases occurred in
the East Coast, Olson said.
Pennsylvania, with 20 cases, had the highest number of illnesses.
Though the outbreak geographically overlaps the _S._ Typhimurium
outbreak somewhat, she said the CDC wasn't aware of any people who
were coinfected with both strains.
Olson said serotype Norfolk as been associated with tomatoes before.
"We're trying to determine how best to prevent this type of
contamination in produce," she noted. A multidrug resistant strain
has been responsible for cases of ground beef contamination in recent
The FDA is working on a traceback investigation to determine the
source of the S Norfolk contamination, Olson said.
[Byline: Lisa Schnirring]
[The posting referred to both serotype Norfolk and Newport, which was
confusing. This Moderator took the liberty of unifying the serotype
names all to Norfolk.
Just as in the other outbreak, there is still no 'smoking tomato'
here. It is notable that salmonellae can survive inside the ripening
tomato, as shown experimentally in the following paper: Guo X, Chen
J, Brackett RE and Beuchat LR: Survival of salmonellae on and in
tomato plants from the time of inoculation at flowering and early
stages of fruit development through fruit ripening. Appl Environ
Microbiol 2001;67: 4760-64.
"The fate of salmonellae applied to tomato plants was investigated. 5
_Salmonella_ serotypes were used to inoculate tomato plants before
and after fruits set, either by injecting stems with inoculum or
brushing flowers with it. Ripe tomato fruits were subjected to
microbiological analysis. Peptone wash water, homogenates of stem
scar tissues, and homogenates of fruit pulp were serially diluted and
plated on bismuth sulfite agar before and after enrichment.
Presumptive _Salmonella_ colonies were confirmed by serological
tests, PCR assay using HILA2 primers, and enterobacterial repetitive
intergenic consensus PCR.
Of 30 tomatoes harvested from inoculated plants, 11 (37 percent) were
positive for _Salmonella_. Of the _Salmonella_-positive tomatoes, 43
and 40 percent, respectively, were from plants receiving stem
inoculation before and after flower set. 2 of 8 tomatoes produced
from inoculated flowers contained_Salmonella_. Higher percentages of
surface (82 percent) and stem scar tissue (73 percent) samples,
compared to pulp of _Salmonella_-positive tomatoes (55 percent),
harbored the pathogen. Of the 5 serotypes in the inoculum, Montevideo
was the most persistent, being isolated from tomatoes 49 days after
inoculation, and Poona was the most dominant, being present in 5 of
11 _Salmonella_-positive tomatoes. Results suggest that _Salmonella_
cells survive in or on tomato fruits from the time of inoculation at
flowering through fruit ripening. Tomato stems and flowers are
possible sites at which Salmonella may attach and remain viable
during fruit development, thus serving as routes or reservoirs for
contaminating ripened fruit." - Mod.LL]
[The timing of the outbreak and knowledge of the outbreak seems a bit
curious. According to the above newswire, the outbreak began in June
2006 and continued through October 2006, with first reporting of the
outbreak on 28 Nov 2006 in the Produce News. It appears as though it
was known about earlier as there were results of a CDC conducted case
control study available. More information on the actual
investigation and timing of notification through the PulseNet system
would be of interest. (Information on the above outbreak is not
available on the CDC foodborne disease website as yet. For those who
are interested in learning more about the PulseNet system, the
website is helpful <http://www.cdc.gov/pulsenet/>). Detection of
multistate outbreaks (or multicountry outbreaks in other regions such
as Europe or South East Asia) is a challenge, especially when the
numbers of reported cases in a defined geographic area may be too
small to really classify as a true outbreak. The use of the
laboratory system for surveillance of these outbreaks is a major
advance and allows for identification of outbreaks that might have
fallen below the "radar screen". This mod is curious to learn more
about the time lag between outbreak occurrence and outbreak
identification through the laboratory surveillance system (such as
PulseNet in the USA). - Mod.MPP]