Outbreak of Multidrug-Resistant
serotype Newport Infections Associated with Consumption of Unpasteurized
Mexican-Style Aged Cheese --- Illinois, March 2006--April 2007
During March 2006--April 2007, an outbreak of
Salmonella enterica serotype Newport infections
occurred predominantly among Hispanics in northeastern Illinois. Samples from 85 patients, one sample of Mexican-style
aged cheese (cotija) from a local Hispanic grocery store (grocery store A), and milk from a bulk tank on a local dairy
farm tested positive for
S. Newport and had indistinguishable pulsed-field gel electrophoresis (PFGE) patterns. This
report summarizes the investigation into
S. Newport infections associated with this outbreak. The findings emphasize the
need for regulatory authorities to ensure that dairy products, including Mexican-style cheese, are manufactured
and distributed by inspected sources and highlight the need for culturally targeted education of consumers and
grocery-store operators regarding risks associated with consuming unpasteurized dairy products.
On October 9, 2006, public health officials in Kane County, Illinois, notified the Illinois Department of
Public Health (IDPH) of 13 cases of
S. Newport infection among Hispanic residents since March 2, 2006.
S. Newport is a rare serotype in Kane County; during 2001--2005, five or fewer infections were reported annually. The Kane
County Department of Health conducted the initial investigation and contacted IDPH for assistance in determining the
source of infection and developing measures to prevent future illness.
By March 1, 2007, local health departments had identified 67 patients who had illnesses compatible with
S. Newport infection. Among these, 46 (69%) reported shopping at
local Hispanic grocery stores. Three stores with the highest reported
shopping frequency (including grocery store A) and the patients' home
addresses were mapped using geographic information system software;
clustering of cases near the stores was apparent. A
hypothesis-generating questionnaire was developed and included
questions regarding consumption of various foods, including
Mexican-style cheese, unpasteurized milk, and unpasteurized and
homemade cheese. The questionnaire was administered beginning March 2,
2007, to patients with onset of illness within the preceding 3 months.
Thirteen patients with an onset during December 30, 2006--February 26,
2007, completed the questionnaire. Ten (77%) reported eating
Mexican-style cheese; none reported consuming unpasteurized milk,
unpasteurized cheese, or homemade cheese 7 days before onset of
Case Definition and Case Finding
A case was defined as diarrheal illness (three or more loose stools within 24 hours) with onset beginning on or
after March 2, 2006, and an isolate of
S. Newport with a PFGE match by at least one enzyme
in an Illinois resident. A memorandum was sent to all local health
departments on November 28 to inform them of the outbreak and encourage
prompt reporting to IDPH. Additional cases were identified by
performing PFGE on all
S. Newport isolate cultures
reported to IDPH. Local Illinois health departments contacted all identified patients to obtain information
regarding demographic characteristics, date of illness onset, clinical presentation, and household contacts.
Patients were asked to report food-consumption and
grocery-shopping history for the 3 days (one incubation period) before illness onset by
use of a standardized Illinois salmonellosis
case report form.
Eighty-five culture-confirmed cases were identified among residents of nine counties in northeastern Illinois,
with dates of illness onset during March 2, 2006--April 25, 2007
Patients ranged in age from 9 days to 85 years (median: 34 years).
Forty-five (53%) were male. Seventy-six (96%) of 79 patients who
reported ethnicity were Hispanic, and Spanish was the primary language
for 40 (78%) of 51 patients who reported a primary language. Among
patients who reported clinical symptoms, 53 (72%) of 74 reported fever,
and 43 (59%) of 73 reported bloody diarrhea. Thirty-six (44%) of 82
patients were hospitalized. No deaths were reported. Five patient stool
isolates were selected randomly and sent to CDC for antibiotic
susceptibility testing. All five isolates were resistant to eight
antibiotics: amoxicillin/clavulanic acid, ampicillin, cefoxitin,
ceftiofur, chloramphenicol, streptomycin, sulfamethoxazole, and
tetracycline. This resistance pattern is consistent with
S. Newport multidrug-resistant phenotype AmpC
After investigators found improperly labeled cotija cheese in
grocery store A, a case-control study was initiated on March 21, 2007.
Case-patients with the most recent onset of illness were contacted
first. Controls were selected through a reverse telephone directory and
matched by age, ethnicity, and city of residence. Twelve case-patients
with onset of illness from November 1, 2006--March 2, 2007, and 27
controls were enrolled. The study included questions about consumption
of four specific types of Mexican-style cheese and purchase of cheese
from 10 local Hispanic grocery stores. Interviews were ended on March
23 because a press release was issued by the Kane County Department of
Health to warn the public, specifically members of the Hispanic
community, about the risks of consuming Mexican-style cheese from
unlicensed producers, an action that might have biased responses. A
matched-pair analysis was performed; no statistical association was
found between illness and cotija or grocery store A (Tables 1 and 2).
During March 6--April 5, 2007, local and state public health food sanitarians inspected Hispanic grocery stores
in Kane County. On March 9, a sanitarian noticed an
improperly labeled Mexican-style aged cheese (cotija) in
grocery store A. The cheese label did not specify the manufacturer or distributor; inspectors were unable to determine
whether the cheese had been obtained from a licensed source. Illinois law requires grocery stores to purchase dairy products
from a licensed manufacturer or distributor
2). An embargo was immediately placed on the cheese, preventing sale to
the public. Cheese samples were sent to the IDPH laboratory for testing. Cotija from grocery store A had >29,400 mU/L
of alkaline phosphatase activity, indicating inadequate pasteurization
3). On March 19,
S. Newport was isolated from
the cheese and had a PFGE pattern indistinguishable from the outbreak strain.
The cotija cheese manufacturer was not identified, so
investigators searched for the source of unpasteurized milk
used to make the cheese. In 2005, dairy farm A had been suspected of illegal sale of unpasteurized milk to grocery store A;
a subsequent investigation was inconclusive. In
Illinois, a dairy producer may sell unpasteurized milk from its farm to
an individual for personal consumption but not for commercial resale
Investigators visited dairy farm A on March 27, collected samples of
unpasteurized milk, and reviewed bulk-milk weight sheets. The data
indicated large variations in pounds of milk sold for pasteurization,
suggesting possible illegal sales of unpasteurized milk. Unpasteurized
milk collected from the bulk tank tested positive for
S. Newport, with a PFGE pattern indistinguishable from the
outbreak strain. On April 5, IDPH prohibited unpasteurized milk sale by farm A to the public until a negative
Salmonella culture was obtained from the bulk milk tank. No additional cases of
S. Newport matching the outbreak pattern were
identified after April 25.
Public Health Action
After the investigation, review of dairy farms' daily bulk-milk weight sheets was heightened by IDPH
inspectors statewide to monitor fluctuations in milk sales that could indicate improper distribution of unpasteurized
milk. Local Illinois health departments were encouraged to visit Hispanic grocery stores and restaurants to ensure
cheese products sold were from licensed dairy manufacturers.
Information on Illinois regulations regarding sale of
dairy products was provided to Hispanic grocery stores. Information was provided to the Spanish-language media to alert
their audience about the risks associated with consumption of
illegally manufactured Mexican-style cheese.
C Austin, DVM, L Saathoff-Huber, MPH, M Bordson, Illinois Dept of Public Health; C Dobbins, MS, C Gross, K Marishta, MPH,
F Carlson, MPH, G Maurice, Kane County Dept of Health;
IC Trevino, DVM, EIS Officer, CDC.
Consumption of unpasteurized dairy products in the United States has been associated with
foodborne illnesses attributed to multiple pathogens, including
Listeria monocytogenes, and
coli O157:H7 (
4--7). During 1998--2005, 45 outbreaks of foodborne illness were reported to CDC in
which either unpasteurized milk or cheese made from
unpasteurized milk was implicated. Approximately 1,000
persons became ill; 104 were hospitalized, and two died (CDC, unpublished data,
Hispanics have a higher incidence of salmonellosis and are more likely
to consume high-risk foods, including unpasteurized milk and cheese,
than other ethnic populations (
Dairy products made with dairy farm A milk were likely responsible for this outbreak. All 85 patients, an
aged Mexican-style cheese (cotija), and raw milk from a local dairy had an isolate of
S. Newport with an indistinguishable PFGE pattern. Although no
significant association was found between consumption of the
Mexican-style aged cheese and illness, no cases of
S. Newport matching the outbreak pattern have been identified since April 25, 2007, and
S. Newport have returned to preoutbreak
levels in Kane County.
Newport-MDRAmpC has become a public health concern because of the increase in reported incidence in the
United States during the last 10 years (
1). Antibiotics typically used to treat
Salmonella infections, especially in children,
are ineffective against this strain (
9). Outbreaks of Newport-MDRAmpC
infection have been associated with an
Italian-style soft cheese and ground beef from dairy cattle
This is the first report of
Salmonella isolated from an aged, rather than fresh, Mexican-style cheese.
Performed correctly, the aging process inhibits pathogenic bacteria such as salmonellae
The Food and Drug Administration allows certain cheeses to be
manufactured using unpasteurized milk if they are aged for at least 60
days.* Although all U.S. dairy manufacturers and distributors are
inspected, requirements for cheese-manufacturing licensure vary among
states. In Illinois, manufacturers must be licensed by the state (
2). Although outbreaks caused by illegally
manufactured Mexican-style cheese have been commonly associated with sales by street vendors, door-to-door salesmen, and
flea markets and with gifts from relatives returning from abroad, small Hispanic grocery stores also have been implicated
To prevent future outbreaks and reduce sales of illegally manufactured cheese, local and state food
regulatory authorities should enforce compliance with unpasteurized milk sale and distribution regulations; dairy farms'
bulk-milk weight sheets should be monitored. Food regulatory authorities should be aware that illegally manufactured
cheese might be sold at grocery stores, be alert for missing or incomplete labeling, and ensure that dairy products are from
an inspected manufacturer or distributor. Finally, food regulatory and public health officials should recognize that
aged Mexican-style cheese can be a source of infection.
This report is based, in part, on contributions by C Conover,
MD, K Kelly-Shannon, P Ward, R Lucht, MBA, D Hennings, Div of
Infectious Diseases, Illinois Dept of Public Health; P Dombroski, J
Price, MS, Div of Laboratories, Illinois Dept of Public Health; and G
Ewald, MSPH, S Greene, MPH, M Lynch, MD, and M Biggerstaff, MPH,
National Center for Zoonotic, Vector-Borne, and Enteric Diseases, CDC.
- CDC. National Antimicrobial Resistance Monitoring System for
enteric bacteria (NARMS): Human isolates final report, 2004.
Atlanta, GA: US Department of Health and Human Services, CDC; 2007.
- Grade A pasteurized milk and milk products act. 410 Illinois compiled statutes 635. Effective October 1, 2003. Available at
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measuring alkaline phosphatase activity in whole milk of multiple
species and bovine dairy drinks: interlaboratory study. J AOAC Int
- D'Aoust JY. Manufacture of dairy products from unpasteurized milk: a safety assessment. J Food Prot 1989;52:906--14.
- Villar RG, Macek MD, Simons S, et al. Investigation of multidrug-resistant
Salmonella serotype typhimurium DT104 infections linked to
raw-milk cheese in Washington State. JAMA 1999;281:1811--6.
- Cody SH, Abbott SL, Marfin AA, et al. Two outbreaks of multidrug-resistant
Salmonella serotype Typhimurium DT104 infections linked
to raw-milk cheese in Northern California. JAMA 1999;281:1805--10.
- MacDonald PD, Whitwam RE, Boggs JD, et al. Outbreak of listeriosis
among Mexican immigrants as a result of consumption of illicitly
produced Mexican-style cheese. Clin Infect Dis 2005;40:677--82.
- Banerjee A, Frierman M; EIP FoodNet Working Group, et al. Characterization of high risk food consumption practices among the
Hispanic population. FoodNet 2000--2001. Chicago, IL: Infectious Diseases Society of America; 2002.
- Gupta A, Fontana J, Crow C, et al. Emergence of multidrug-resistant
Salmonella enterica serotype Newport infections resistant to
expanded-spectrum cephalosporins in the United States. J Infect Dis 2003; 188:1707--16.
- Bachmann HP, Spahr U. The fate of potentially pathogenic bacteria
in Swiss hard and semihard cheeses made from raw milk. J Dairy Sci
* Food and Drug Administration, Center for Food Safety and
Applied Nutrition. Grade "A" pasteurized milk ordinance: 2003 revision.
Available at http://www.cfsan.fda.gov/~ear/pmo03toc.html.
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