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Published Date: 2002-11-23 23:50:00
Subject: PRO/AH/EDR> Salmonella poona, cantaloupes - USA, Canada (02)
Archive Number: 20021123.5884

SALMONELLA POONA, CANTALOUPES - USA, CANADA (02)
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Date: 24 Nov 2002
From: ProMED-mail <promed@promedmail.org>
Source: Morbidity and Mortality Weekly Report [edited]
<http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5146a2.htm>

Multistate Outbreaks of Salmonella Serotype Poona Infections Associated
with Eating Cantaloupe from Mexico --- United States and Canada, 2000--2002
-------------------------------------------------
In the spring of consecutive years during 2000-2002, 3 multistate outbreaks
of _Salmonella [enterica - Mod. LL] serotype _Poona_ infections associated
with eating cantaloupe imported from Mexico occurred. In each outbreak, the
isolates had indistinguishable pulsed-field gel electrophoresis (PFGE)
patterns; the patterns observed in the 2000 and 2002 outbreaks were
indistinguishable, but the pattern from 2001 was unique among them.
Outbreaks were identified first by the California Department of Health
Services (2000 and 2001) and the Washington State Department of Health
(2002) and involved residents of 12 states and Canada. This report
describes the investigations, which led ultimately to an import alert on
cantaloupes from Mexico. To limit the potential for cantaloupe
contamination, the Food and Drug Administration (FDA) continues to work
with the Mexican government on a food-safety program for the production,
packing, and shipping of fresh cantaloupes.
April--June 2000 Outbreak
A total of 47 confirmed cases of _S. Poona_ infections with
indistinguishable PFGE patterns were identified from California (26),
Washington (10), Nevada (5), New Mexico (3), Oregon (2), and Colorado (1),
with illness onset occurring during 14 Apr- 2 Jun 2002. The median age of
ill persons was 7 years (range: 1-95 years); 28 (60 percent) patients were
aged <10 years, and 9 (19 percent) were aged >60 years. 24 (51 percent)
patients were male and 9 (19 percent) were hospitalized.
A matched case-control study was conducted; 20 case-patients were matched
by age category to 37 community controls. A case was defined as
laboratory-confirmed infection with _S. Poona_ of the outbreak PFGE pattern
in a person with illness onset during April--June. By multivariable
modeling, illness was associated only with eating cantaloupe (matched odds
ratio [MOR]=6.7; 95 percent confidence interval [CI]=1.3-34.0), with 16 (80
percent) case-patients versus 7 (19 percent) controls reporting eating
cantaloupe. Cantaloupe was purchased either pre-cut or whole.
April-May 2001 Outbreak
In April 2002, an initial cluster of _S. Poona_ was identified in
California. Isolates had a rare biochemical trait, the inability to produce
hydrogen sulfide (H2S), and PFGE patterns that were indistinguishable. A
total of 50 cases of H2S-negative _S. Poona_ infections were identified in
residents of California (28), Washington (8), Nevada (7), Arizona (6), and
Oregon (1).
Demographic and illness-history data from the 28 California patients
indicated that illness onset occurred during 6 Apr - 28 May 2002. The age
distribution was bimodal; the 19 children had a median age of 3 years
(range: 1-5 years) and the 9 adults had a median age of 80 years (range:
39-91 years). 15 (54 percent) patients were female. 10 (36 percent)
patients were bacteremic; 1 infant girl had _S. Poona_ isolated from a
urine specimen. 9 (33 percent) patients were hospitalized, and 2 patients
(a man aged 78 years and a woman aged 91 years) died with Salmonella
septicemia.
A matched case-control study was conducted; 11 case-patients from
California (7), Nevada (2), Arizona (1), and Washington (1) were matched by
age category to 19 community controls. Case-patients had
laboratory-confirmed infections of the outbreak strain of H2S-negative _S.
Poona_ and illness onset during the first 2 weeks of April 2002. Illness
was associated only with eating cantaloupe (MOR=7.4; 95 percent
CI=1.0--178.0). 8 (80 percent) case-patients and 6 (33 percent) controls
recalled eating cantaloupe. Cantaloupe was purchased either pre-cut or whole.
March-May 2002 Outbreak
A total of 58 cases with _S. Poona_ isolates with indistinguishable PFGE
patterns were identified in California (21), Washington (9), Oregon (5),
British Columbia (4), Colorado (3), Nevada (3), Manitoba (2), Missouri (2),
Ontario (2), Saskatchewan (2), Texas (2), Arkansas (1), Minnesota (1), and
Vermont (1). Illness onset occurred during 30 Mar - 31 May 2002; the median
age of patients was 6 years (range: 4 months-91 years); 32 (55 percent)
were aged <10 years, and 11 (19 percent) were aged >60 years. A total of 31
(55 percent) were female. 10 patients were hospitalized.
A matched case-control study was conducted; 27 case-patients were matched
by age category to 54 community controls. A case was defined as _S. Poona_
infection with the outbreak PFGE pattern in a person aged >2 years with
illness onset during 15 Mar - 3 May 2002. The only exposure significantly
associated with illness was eating cantaloupe; 20 (74 percent)
case-patients recalled eating cantaloupe compared with 11 (20 percent)
controls (MOR=15.5; 95 percent CI=3.3-125.0). Case-patients (50 percent)
were more likely than controls (13 percent) to eat cantaloupe purchased
whole (MOR=5.8; 95 percent CI=1.6-23.3) or to eat cantaloupe in a fruit
salad or as a garnish (28 percent versus 5 percent) (MOR=6.5; 95 percent
CI=1.2-63.0). No other factors were significantly associated with illness.
Traceback and Regulatory Action
FDA, in conjunction with state and provincial food regulatory agencies,
conducted traceback investigations of cantaloupe purchased by patients in
all 3 outbreaks. In each instance, point-of-sale sources of cantaloupe were
traced back to shippers and then to farms in Mexico. In response to the
2000 and 2001 outbreaks, FDA conducted on-farm investigations in Mexico and
concluded that measures were not in place to minimize microbial
contamination in the growing, harvesting, packaging, and cooling of cantaloupe.
Possible sources of contamination include irrigation of fields with water
contaminated with sewage, processing (cleaning and cooling) produce with
Salmonella-contaminated water, poor hygienic practices of workers who
harvest and process the cantaloupe, pests in packing facilities, and
inadequate cleaning and sanitizing of equipment that comes in contact with
cantaloupe. In association with the 2001 outbreak, FDA detained product
imported by the shipper on 31 May 2002, and the shipper voluntarily
recalled its imported Mexican cantaloupe. The shipper and the implicated
farm in Mexico remain on detention. In association with the 2002 outbreak,
the importer voluntarily recalled the implicated Mexican cantaloupe, and
FDA placed the implicated farms on detention. On 28 Oct 2002, FDA issued an
import alert on cantaloupe from Mexico that detains all products offered
for entry at all U.S. ports.
Editorial Note:
Salmonella infections have been linked to melons at least since 1990 when
Salmonella serotype Chester traced to cantaloupe caused 245 illnesses in 30
states. The cantaloupe were imported from either Mexico or Guatemala. In
1991, an outbreak of cantaloupe-associated _S. Poona_ infections caused 400
illnesses in 23 states. Illness was associated with eating pre-cut
cantaloupe in fruit salads or from salad bars. Although industry sources
identified the lower Rio Grande Valley in Texas as the probable source of
the implicated cantaloupe, some might have come from Mexico.
In response to this outbreak, FDA conducted a microbiologic survey that
isolated a variety of Salmonella serotypes from approximately 1 percent
of sampled imported cantaloupe and watermelon. In 1997, an outbreak of
Salmonella serotype Saphra infections affected 25 persons in California.
Illness was associated with cantaloupe imported from Mexico. After the 2000
and 2001 _S. Poona_ outbreaks, FDA conducted farm investigations in Mexico,
issued press releases to warn consumers, placed implicated farms on
detention, and conducted sampling surveys of imported cantaloupe. The 1999
and 2000 FDA surveys of imported produce indicated that 5 percent of
cantaloupe sampled (8 of 151) was contaminated with Salmonella. A 2001
survey of imported produce indicates that of 29 cantaloupes from Mexico
tested, none yielded Salmonella, Shigella, or _Escherichia coli_ O157:H7
(FDA, unpublished data, 2001). The interpretation of the 2001 survey is
limited by of the small sample size.
_S. Poona_ is a relatively rare serotype that is responsible for 1 percent
of human Salmonella isolates reported in the United States in 2001;
however, of the 6 cantaloupe-associated Salmonella outbreaks, 4 were
attributed to infections with _S. Poona_. Typically, human infection with
_S. Poona_ is associated with reptile exposure. The 3 outbreaks attributed
to _S. Poona_-contaminated cantaloupe traced to Mexican farms suggest the
possibility of a unique natural reservoir in the Mexican farm environment,
possibly from reptiles such as iguanas drawn to feed on melon crops that
enter the packing sheds and contaminate the equipment. Subsequently, water
used in the washing and cooling process might spread the contamination.
FDA provides information about the decontamination of melons to the retail
industry, food-service establishments, and commercial processors of pre-cut
melon. The use of sodium hypochlorite or other permitted antimicrobials in
combination with brushing is recommended. The potential for microbial
contamination also might be reduced by using only good-quality fruit that
is free from open wounds or defects that might allow bacteria to
contaminate the interior of the fruit.
Additional research is needed to determine the effectiveness of consumer
produce-washing practices. Consumers should be sure that fresh-cut melons
are refrigerated or surrounded by ice; leftover cut melons should be
discarded if left at room temperature for >2 hours. Additional information
for consumers is available at
<http://www.fda.gov/bbs/topics/answers/2002/ans01167.htm>
On 28 Oct 2002, in response to the 3 outbreaks during 2000-2002 and
analytical results from the sampling of imported Mexican cantaloupe, FDA
issued an import alert that detains all cantaloupe from Mexico offered for
entry at all US ports. FDA will continue to work with the Mexican
government on a food-safety program for the production, packing, and
shipping of fresh cantaloupe. The Mexican government is developing a
certification program based on sound agricultural and manufacturing
practices that would allow FDA to identify farms that have adopted and
implemented such a food-safety program.
--
ProMED-mail
<promed@promedmail.org>
[The current action of banning imports of fruit from a country following
multiple foodborne outbreaks over the period of more than one year is not
without precedence. In 1996/1997 there were multiple outbreaks of
cyclosporiasis associated with raspberries imported from Guatemala that
lead to a ban on import of raspberries from Guatemala
for 1998 (in 1998 Canada had another outbreak associated with raspberries
from Guatemala and a ban on import was placed there as well) (See
ProMED-mail postings below for 1996/1997/1998).
The FDA food alert on imported canteloupes from Mexico was issued on 28 Oct
2002 and can be found at:
<http://www.fda.gov/bbs/topics/ANSWERS/2002/ANS01167.html> - Mod.MPP]

See Also