MSP2

Salmonella in the Caribbean

Modifed from “Stehr-Green, J., Caribbean Epidemiology Centre: Pan American Health Organization, World

Health Organization, & Centers for Disease Control and Prevention. (2016, April 14).

Epidemiologic Case Studies (Rep.). Retrieved from

https://www.cdc.gov/epicasestudies/classroom_salmonella.html”

Original investigators: Lisa Indar-Harrinauth, 1, 2

Nicholas Daniels, 3

Parimi Prabbakar, 1

Clive

Brown, 1

Gail Baccus-Taylor, 2

Edward Commissiong, 2

H. Reid, 4

and James Hospedales 1

1 Caribbean Epidemiology Centre, Pan American Health Organization/World Health Organization

2 Food Technology Unit, Department of Chemical Engineering, University of the West Indies

3 Foodborne and Diarrheal Diseases Branch, Division of Bacterial and Mycotic Diseases, National

Center for Infectious Diseases, Centers for Disease Control and Prevention 4 Trinidad Public Health Laboratory, Trinidad

Case study and instructor’s guide created by: Jeanette K. Stehr-Green, MD

Reviewed by: Frederick J. Angulo, DVM, PhD, Stephanie M. DeLong, MPH, Lisa Indar-

Harrinauth, PhD, MSc, James Hospedales, MBBS, MSc, MFPHM, Robert Tauxe, MD, MPH,

James Flint, MPH, Roderick C. Jones, MPH, Eleni Galanis, MD, MPH

NOTE: This case study is based on real-life investigations undertaken in Trinidad and

Tobago in 1998-1999 and published in Clinical Infectious Diseases and the West Indian

Medical Journal. (See Appendix for abstracts.) Some aspects of these investigations

(and the circumstances leading up to them) have been altered to assist in meeting the

desired teaching objectives and some details have been fabricated to provide continuity

to the storyline.

Target audience: public health practitioners with knowledge of basic epidemiologic concepts, especially

non-epidemiologists (e.g., laboratorians, environmental health specialists, sanitarians, public health

nurses, veterinarians, MPH students)

Training materials funded by: the Centers for Disease Control and Prevention (National Center for

Infectious Diseases, Food Safety Initiative, Public Health Practice Program Office, and Epidemiology

Program Office/Division of International Health)

August 2004

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention Atlanta, Georgia 30333

Salmonella in the Caribbean

Part I – Background on Salmonella

Salmonellosis is a gastrointestinal illness caused by bacteria from the genus Salmonella. The illness is

characterized by the sudden onset of headache, abdominal pain, diarrhea (which may be bloody), nausea,

and sometimes vomiting. Fever is almost always present. The illness typically lasts for 5-7 days and

usually does not require treatment unless the patient becomes severely dehydrated or the infection spreads

from the intestines. In the immunocompromised host or an overwhelming infection in a normal host,

Salmonella may spread to the blood stream and other body sites, and can cause death unless treated

promptly with antibiotics.

Salmonella live in the intestinal tracts of humans and other animals, including mammals, birds, and

reptiles. Salmonella are usually transmitted to humans by eating foods contaminated with animal feces.

Implicated foods are typically those of animal origin, such as beef, poultry, milk, or eggs, but all foods,

including vegetables, may become contaminated. The incubation period for salmonellosis is usually 12-

36 hours, but can be as long as a week.

Figure 1. Salmonella surface antigens The genus Salmonella consists of only

two species: S. enterica and S. bongori.

The latter species, however, is very rare.

Members of the species Salmonella

enterica can be divided into smaller

groups (i.e., serotypes) based on two

structures on the cell surface: the O

antigen and the H antigen. The O

antigen is a carbohydrate antigen in the

lipopolysaccharide of the bacterium’s

outer cell membrane. The H antigen is a

protein antigen in the bacterium’s

flagella. (Figure 1)

O antigens and H antigens are detected

using antisera that react with a single

antigen or group of related antigens. All Salmonella serotypes can be designated using a formula based

on the O and H antigens they express. Many serotypes are also given a name (e.g., Salmonella

Typhimurium, Salmonella Agona, Salmonella Muenchen). (NOTE: The serotype name is capitalized

and not italicized.)

Although extensive serotyping of surface antigens can be used for identification of a Salmonella isolate,

the reagents are costly, the process is time-consuming, and the results are not likely to affect treatment of

the individual patient. As a result, in many countries clinical laboratories perform only a few O antigen

reactions that allow them to group an isolate into broader, less specific categories called serogroups. The

isolate is then forwarded to a state or national reference laboratory for complete serotyping.

There are over 2,500 recognized Salmonella serotypes. In 1995, Salmonella Enteritidis, Typhimurium,

and Typhi accounted for over three-quarters of the isolates reported in a global survey.

Part II – Surveillance of Salmonella in the Caribbean

As early as the mid-1980s, Salmonella became a pathogen of public health concern in the Caribbean

(Figure 2) when it caused an increasing number of cases and outbreaks of diarrhea involving local and

tourist populations. The communicable disease surveillance system in place at the time, however, did not

support the timely detection of these outbreaks or the investigation of risk factors associated with

infection. As a result, the incidence of Salmonella continued to grow.

Figure 2. Countries of the Caribbean and surrounding land masses.

The communicable disease surveillance system in the Caribbean was based on notifiable disease reports

from physicians and other health care providers in the community (i.e., clinician-based reporting).

Surveillance of most communicable diseases included both laboratory-confirmed cases and cases

diagnosed based on clinician suspicion. The laboratory did not report cases of communicable disease to

the surveillance system or submit isolates for confirmation or further testing (e.g., serotyping).

To report a communicable disease in the Caribbean, the health care provider completed a disease report

card (Figure 3) and mailed it to the local health department within 7 days of diagnosis of the patient.

Figure 3. Communicable Disease Case Report Card

CARIBBEAN EPIDEMIOLOGY CENTRE

Clinician-based Reporting COMMUNICABLE DISEASE CASE REPORT CARD

Case identification Last name, First name, Middle initial:

Address:

City/Country:

Disease information Diagnosis: Lab-confirmed: _ Yes _ No Date of onset:

Case information Sex: _ Male _ Female Age: Current status: _ Alive _ Dead

Attending physician Name: Address: Telephone number:

Person reporting case (if not attending physician) Name: Telephone number:

A clerk at the local health department reviewed the report cards for completeness (requesting additional

information from the health care provider, where needed), batched the reports, and mailed them to the

country’s Ministry of Health where they were sorted by disease. The Ministry of Health forwarded the

reports to the Caribbean Epidemiology Centre (CAREC).

An epidemiologist from CAREC reviewed and summarized the reports from the individual countries. If

necessary, the epidemiologist contacted the Ministry of Health if an unusual disease pattern was noted.

CAREC distributed weekly, quarterly, and annual communicable disease reports for the region and each

country to all Ministries of Health. In addition, CAREC reported occurrences of selected diseases (e.g.,

cholera, plague, yellow fever) to the Pan American Health Organization/World Health Organization as

required by International Health Regulations.

In an evaluation of the Caribbean communicable disease surveillance system, it was determined that less

than 40% of notifiable disease cases were actually reported by health care providers. The average

reporting delay (i.e., from diagnosis to receipt of the report by CAREC) was 56 days.

After extensive consultation with the Ministries of Health from the individual Caribbean countries, health

care providers, professional medical organizations, and clinical laboratories, CAREC proposed a

modification of communicable disease reporting in the region.

In addition to health care providers (i.e., clinician-based surveillance), clinical laboratories were enlisted

to report the detection of notifiable diseases that were laboratory confirmed (i.e., laboratory-based

surveillance). Clinical laboratories were also asked to forward all isolates of Salmonella to the national

reference laboratory in Trinidad (i.e., the Public Health Laboratory). Staff at the Public Health

Laboratory, who had specialized training in Salmonella serotyping and access to specialized reagents,

were to perform serotyping and antimicrobial susceptibility testing on forwarded Salmonella isolates.

To further improve the timeliness of reporting, health care providers and clinical laboratories were to

submit reports directly to newly designated surveillance officers in each country’s Ministry of Health.

Diseases that potentially could be spread through food or water or readily from person-to-person were to

be reported within 24 hours of diagnosis. The remainder were to be reported within 3 days of diagnosis.

Health care providers and clinical laboratories were encouraged to submit reports by telephone or FAX.

Initial acceptance and implementation of the new communicable disease reporting procedures were slow.

Member countries had limited public health resources to initiate the changes and there was resistance

among health care providers and clinical laboratories.

Staff from CAREC visited member countries and, with the assistance of staff from the local Ministry of

Health, provided training to both health care providers and staff from clinical laboratories. Training

focused on the mechanics of reporting and how surveillance data would be used to monitor disease trends,

detect outbreaks, and initiate controls measures. Many of the presentations were made at professional

meetings, allowing for an open discussion of the reporting procedures and surveillance in general.

CAREC staff toured the larger clinical laboratories in the various countries and identified problems

associated with testing, reporting, and the forwarding of Salmonella isolates to the national Public Health

Laboratory in Trinidad. A resource person was identified at the Public Health Laboratory to provide

ongoing support to all clinical laboratories.

A close working relationship developed between the Public Health Laboratory in Trinidad and CAREC.

Laboratory staff forwarded laboratory results to epidemiologists at CAREC on a weekly basis and

notified them by phone if an unusual case was noted or an increase in the isolation rate of a particular

disease occurred.

CAREC staff summarized communicable disease surveillance results (including serotype and

antimicrobial susceptibility test results) and distributed a weekly summary to the Ministries of Health and

monthly updates to health care providers and clinical laboratories. They worked closely with staff from

the respective Ministries of Health if an unusual disease pattern was noted or some reporting problem

became evident.

Part III – Descriptive Epidemiology of Salmonella in Trinidad

Due to the close proximity of both CAREC and the national Public Health Laboratory, Trinidad and

Tobago moved most quickly on the implementation of the new reporting procedures. As a result, several

large outbreaks of salmonellosis were detected allowing local public health practitioners to initiate

investigations and implement appropriate control measures. However, salmonellosis continued to occur

at a high rate in the country.

In 1998, CAREC summarized the following data for laboratory-confirmed cases of salmonellosis reported

in Trinidad and Tobago.

Table 1. Laboratory isolates of Salmonella by serotype and year of diagnosis,

Trinidad and Tobago, 1988-1997.

Serotype

Year of Diagnosis

88 89 90 91 92 93 94 95 96 97

Enteritidis 0 0 0 0 10 12 28 57 117 83

Typhimurium 14 16 19 27 94 55 47 23 21 15

Other 37 28 37 58 31 47 54 59 67 41

TOTAL 51 44 56 85 135 114 129 139 205 139

Due to the increase in S. Enteritidis in Trinidad and Tobago, CAREC focused their analyses on this

serotype. The following data are for S. Enteritidis only.

From 1995-97, 257 laboratory-confirmed cases of S. Enteritidis infection were reported in Trinidad and

Tobago. Approximately, 86 cases were reported each year for an annual incidence of 6.8 per 100,000

population. In general, the geographic distribution of patients with S. Enteritidis infection reflected

population distributions on the two islands. The largest numbers of cases were reported from the most

populous counties of St. George and Victoria. An average of 4 people died each year from salmonella

infection.

A similar proportion of S. Enteritidis infections occurred among males (48%) and females (52%).

However, the distribution of cases varied by age group (Figure 4) and month of diagnosis (Figure 5).

Figure 4. Laboratory-confirmed cases of Salmonella Enteritidis (per 100,000 population)

by age group and year of diagnosis, Trinidad and Tobago, 1995-1997.

Figure 5. Laboratory-confirmed cases of Salmonella

Enteritidis by month and year of diagnosis, Trinidad and

Tobago, 1995-1997.

Part IV – Case-Control Study of S. Enteritidis in Trinidad and Tobago

To explore risk factors for S. Enteritidis infection in Trinidad and Tobago, a matched case-control study

was undertaken from March 1998 - May 1999. A case-control study design was used because the cases

did not arise from a well-defined group of people and were distributed across the entire country.

Cases were patients with laboratory-confirmed S. Enteritidis infection who were reported through the

communicable disease surveillance system. Cases were enrolled prospectively, shortly after diagnosis.

Controls were persons with no diarrheal illness in the previous 4 weeks who lived in the same

neighborhood as cases and were similar in age. Investigators attempted to enroll two controls for each

case.

Using a standardized questionnaire, investigators collected information from cases about foods and

beverages consumed, recent travel, and food handling practices in the 3 days before they became ill.

Controls were asked about these exposures during the same 3-day period as the matched case. The

questionnaire was administered to both cases and controls by one of the investigators in face-to-face

interviews.

Forty-five patients and 92 controls were enrolled in the case-control study. The investigators analyzed the

results of the case-control study.

In the Trinidad and Tobago case-control study, cases and controls were similar to each other in terms of

age, sex, ethnic distribution, and place of residence. Exposure to potential sources of Salmonella,

however, differed between cases and controls (Table 2).

Table 2. Potential sources of exposure to Salmonella, Trinidad and Tobago

Case-Control Study, March 1998 – May 1999.

Exposure* Matched Odds Ratio p-value

Ate chicken 0.5 0.4

Ate shell eggs 8.8 <0.001

Ate dishes that contained raw

or undercooked eggs

18.9 0.001

Ate ground beef 1.3 0.6

Ingested powdered milk 1.5 0.2

Exposed to live chickens 1.3 0.4

Bought refrigerated eggs 0.1 <0.001

Refrigerated eggs at home 0.03 <0.001 *in the 3 days before onset of illness in the associated case

The specific raw egg-containing foods that were implicated by the case patients’ food histories included

homemade eggnog, cake batter, homemade ice cream, punch a crème (i.e., a drink similar to eggnog), and

stout and eggs. The implicated food items correlated with the predominance of cases in December and

January as many of these foods are consumed more frequently in the holiday season.

Samples of the implicated foods were collected from patients, from the places where patients had

originally purchased the foods, or both and were cultured for Salmonella. S. Enteritidis isolates from

patients and food were phage-typed at the U.S. Centers for Disease Control and Prevention (CDC) in

Atlanta, Georgia.

S. Enteritidis samples from 34 patients were selected for phage typing. Of these, 30 (88%) were found to

be phage type 4 and 4 (12%) were found to be phage type 1. S. Enteritidis was isolated from 15 (45%) of

the 33 food samples implicated by the patients’ food histories. Nine of the 15 food isolates were phage

typed; all nine were phage type 4.

Part V – Study of Eggs in Trinidad

To further investigate the role that eggs may play as a source of Salmonella infections in Trinidad, a

microbiologic survey of shell eggs was undertaken. Ten egg-producing farms across the country were

selected, nine of which were the largest and most popular commercial table egg farms in Trinidad. Their

total production accounted for approximately 75% of the country’s egg supply.

Twenty-five freshly laid eggs were collected from each farm on three different occasions for a total of

750 eggs. Each set of 25 eggs was cultured for Salmonella in pooled batches.

Eggshells were cultured separately from egg contents. The eggshell samples were prepared by swabbing

the shell surface of each of the 25 eggs with cotton wool tips moistened with lactose pre-enrichment

broth. The eggs were not washed prior to swabbing. The eggs were then sanitized using U.S. Food and

Drug Administration eggshell disinfection procedures: each egg was cleaned with a stiff wire brush, hand

washed under running water with antibacterial soap, and patted dry with a paper towel. The eggs were

then placed in a wire basket and immersed in 70% alcohol for 30 minutes followed by distilled water for

10 minutes. The eggs were then allowed to air dry. The contents were removed aseptically, pooled

together, and homogenized in a blender.

Salmonella was detected more often in shell cultures (4.6% of samples) than in content cultures (1.2% of

samples). S. Typhimurium was the most prevalent serotype found on the eggshells and S. Enteritidis was

the most prevalent serotype isolated from the egg contents (Table 3).

Table 3. Salmonella serotypes isolated from the 750 pooled eggshells and egg contents

from 10 egg-producing farms, Trinidad, 1998-1999.

Salmonella serotype isolated

Percent positive for serotype*

Pooled eggshells Pooled egg contents

S. Typhimurium 3.06 0.4

S. Enteritidis 0.67 0.8

S. Ohio 0.27 -

S. Cerro 0.27 -

S. Infantis 0.27 -

S. Heidelberg 0.13 -

Total 4.6 1.2 *Because Salmonella isolates are generally present in very low numbers in eggs, it was assumed that each isolate came from one positive egg and the percentage was based on a denominator of 750.

The isolation rates of Salmonella on shell surfaces and in egg contents varied among the 10 egg-

producing farms. At least one serotype of Salmonella was isolated from eggshells at all 10 of the farms.

Salmonella was isolated from egg contents at only three of the farms.

An environmental health assessment was undertaken at each of the farms by a food safety officer from the

Trinidad and Tobago Ministry of Agriculture to identify factors that could have contributed to the

contamination of eggshells and contents with Salmonella.

The food safety officer inspected the farms and collected information about the system of chicken rearing,

quality control measures, feed and litter type, egg cleanliness, and other management practices.

At four of the farms, the environment and immediate surroundings were generally clean with dry litter

surfaces and clean drinking water, poultry houses, nesting boxes, and equipment. Proper egg-handling

techniques and good farm practices were also employed. The eggs collected from these farms appeared

clean with little or no fecal matter on their surfaces.

In contrast, the surroundings of the other six egg-producing farms generally appeared unsanitary: litter

surfaces were wet on most occasions. Egg belts, poultry houses, and nesting boxes were dirty and there

were rodents and flies. These farms were also characterized by odor build-up, such as ammonia, and the

eggs collected from them frequently had feces and sometimes blood on the shells. In general, these farms

had higher Salmonella isolation rates from pooled eggshells and egg contents than the other farms.

None of the 10 farms had routine microbial monitoring of their flocks or eggs.

Part VI - Prevention and Control

Following release of the results from the S. Enteritidis case-control study, the microbiologic survey of

shell eggs, and environmental health assessments of egg-producing farms, the Trinidad and Tobago

Ministries of Health and of Agriculture initiated a farm-to-table approach to Salmonella prevention and

control strategies. These strategies combined public health education of consumers, food service

establishments, and food workers (on the risks associated with eating raw and undercooked eggs and

using unrefrigerated eggs) and strategies for reduction of Salmonella infections among egg-laying flocks

and breeder flocks.

Regional workshops were held in November 2002 for egg producers on production and food safety.

“Good Agricultural Practices” for hatchery sanitation and egg production were developed from the

proceedings. Drafts were widely distributed for review and comment. Final copies were distributed to all

egg-producing farms under the coordination of the Inter-American Institute for Cooperation on

Agriculture. The Ministry of Agriculture, responsible for the regulation of food safety in Trinidad and

Tobago, made staff available on an ongoing basis to answer questions from producers on the “Good

Agricultural Practices” and help them to explore and solve problems.

Through public and private partnerships and networking, Ministry of Agriculture officials developed a

protocol to identify and remove infected flocks from the egg supply and increase quality assurance and

sanitation measures at egg-producing farms. The procedures included the following steps:

 Both eggs and chickens from commercial egg-producing farms will be tested for Salmonella on a quarterly basis.

 Any flocks that test positive for Salmonella on routine exam will be re-tested.

 If a second sample is positive, traceback investigations will be undertaken to identify breeder flocks.

 Infected breeder flocks (those that produced the egg-laying chickens) will be slaughtered.

 Eggs from infected egg-laying chickens will be pasteurized instead of being sold as shell eggs.

 Non-infected flocks from farms at which infected flocks have been detected will be tested more frequently (i.e., every 4 weeks).

The Ministry of Agriculture implemented the above procedures in Trinidad and Tobago in 2003.

In 2004, the Ministry of Agriculture took additional efforts to prevent the occurrence of salmonella by

implementing strategies to reduce the prevalence of the disease and stop the transmission across the

population. Specifically, the Ministry of Health implemented strategies to increase the timeliness of

reporting salmonella cases. With the initiative, the position of “Surveillance Officer” was created, and

surveillance officers were hired for each country’s Ministry of Health. The new protocol required health

care providers and clinical laboratories to submit reports of disease detection directly to the surveillance

officer, ensuring a specific individual is in charge of tracking the occurrence and prevalence of the

diseases. In addition, diseases that potentially could be spread through food or water, or readily from

person-to-person, were to be reported within 24 hours of diagnosis. The remainder were to be reported

within 3 days of diagnosis. Health care providers and clinical laboratories were encouraged to submit

reports by telephone or FAX.

In 2006, the Ministry of Agriculture further expanded their prevention strategy by offering treatment for

the disease. Although antibiotics are not usually required for a salmonella outbreak as most people recover

on their own within a week, there are extreme cases in which antibiotics may be necessary. Previously,

antibiotics were not designated for salmonella outbreaks, but with the new initiative, those with severe

cases of salmonella are able to access antibiotics for their treatment. In addition, the Ministry of

Agriculture has strengthened their communication to the community around common treatment options for

the disease, and strategies for alleviating common symptoms. Specifically, there has been a campaign

educating parents and children on the importance of hydration when affected by salmonella, and the

dangers of dehydration, which is one of the most dangerous aspect of salmonella.

Epilogue

Serotyping of Salmonella, as used in the investigation of Salmonella Enteritidis in the Caribbean, is a

common subtyping procedure used throughout the world. In a 1997 survey of World Health Organization

(WHO) member states, 69 of the responding 104 countries conducted Salmonella serotyping as part of

public health surveillance for salmonellosis. Serotyping was performed in all six WHO regions; however,

surveillance was limited in time or scope for some countries. Access to serotyping reagents varied by

country and some countries reported only serogroup results.

WHO Global Salm-Surv, an international, foodborne disease surveillance network, was created by WHO

in partnership with the Danish Institute for Food and Veterinary Research, the Centers for Disease

Control and Prevention, Institut Pasteur International Network, Health Canada, and the Animal Sciences

Group (ID-Lelystad) in the Netherlands. The goal of WHO Global Salm-Surv is to reduce foodborne

diseases through enhancement of laboratory-based surveillance (including serotyping and antimicrobial

resistance testing) and outbreak detection and response techniques. Components of the network that help

promote this goal include international training courses, an external quality assurance system, and country

and region-specific projects. The network also offers a moderated list serv, web-based annual Salmonella

summary data from member institutions, and a website, and provides services such as reference testing

and identification of reliable sources of antisera for countries.

As of November 2003, WHO Global Salm-Surv had members from 138 countries including the Bahamas,

Barbados, Belize, Dominican Republic, Jamaica, Saint Lucia, Suriname, and Trinidad and Tobago in the

Caribbean. Participation in WHO Global Salm-Surv has provided critical information to investigate

outbreaks such as the one described in this case study and has led to local interventions that have reduced

the human health burden of Salmonella and other foodborne diseases globally.

Figure 6. WHO Global Salm-Surv Country Membership

References

Herikstad H, Motarjemi Y, Tauxe RV. Salmonella surveillance: a global survey of public health

serotyping. Epidemiol. Infect 2002;129:1-8.

Indar-Harrinauth L, Daniels N, Prabhakar P, Brown C, Baccus-Taylor G, Comissiong E, Hospedales J.

Emergence of Salmonella enteritidis phage type 4 in the Caribbean: Case-control study in Trinidad

and Tobago, West Indies. Clinical Infectious Diseases 2001;32:890-6. (See Appendix for abstract.)

Indar L, Baccus-Taylor G, Commissiong E, Prabhakar P, Reid H. Salmonellosis in Trinidad: evidence for

transovarian transmission of Salmonella in farm eggs. West Indian Med J 1998;47:50-3. (See

Appendix for abstract.)

Orrett FA and Shurland SM. Susceptibility patterns and serotypes of non-typhoidal Salmonella inTrinidad.

Saudi Med J 2001;22:852-5.

Appendix: Abstracts from Original Investigations

Indar-Harrinauth L, Daniels N, Prabhakar P, Brown C, Baccus-Taylor G, Comissiong E,

Hospedales J. Emergence of Salmonella enteritidis phage type 4 in the Caribbean: Case-

control study in Trinidad and Tobago, West Indies. Clin Infect Dis 2001;32(6):890-6.

A prospective case-control study involving 46 case patients and 92 age- and neighborhood-matched

control subjects was conducted in Trinidad and Tobago (T&T) between March 1998 and May 1999 to

determine the etiology, sources, and risk factors for Salmonella enteritidis (SE) infection. SE infection in

T&T was found to be associated with the consumption of shell eggs, and in particular raw or undercooked

eggs. SE isolates from 30 (88%) of 34 patients and from 9 implicated egg or egg-containing food

samples were phage type 4. Homemade eggnog and ice cream, cake batter, and egg-containing beverages

were the main raw egg-containing foods, reflecting the cultural practices of the people of T&T. Public

health education on the risks of eating raw or undercooked eggs, thorough cooking of all egg dishes, and

refrigeration of shell eggs and egg dishes; studies tracing infected eggs to their sources; and testing of

flocks of layer chickens for SE are needed to reduce the incidence of this infection.

Indar L, Baccus-Taylor G, Commissiong E, Prabhakar P, Reid H. Salmonellosis in Trinidad:

Evidence for transovarian transmission of Salmonella in farm eggs. West Indian Med J

1998;47(2):50-3.

The aim of this study was to determine whether the contents of farm eggs in Trinidad are contaminated

with Salmonella and if transovarian transmission occurs. 750 fresh eggs from 10 farms supplying 75% of

the country's eggs were cultured for Salmonella. Salmonella was found on the egg shells' surfaces from

all farms, and in the egg contents from three farms. Isolates were obtained from the cultures of the

contents and shells of nine (1.2%) and 35 (4.66%) eggs, respectively (p < 0.005). Serotypes found in the

contents were S. enteritidis (0.8%; deduced to be contaminated by transovarian transmission) and S.

typhimurium (0.4%); those isolated from the shells (contaminated by faecal transmission) were S.

typhimurium (3.06%), S. enteritidis (0.67%), S. ohio (0.27%), S. cerro (0.27%), S. infantis (0.27%) and S.

heidelberg (0.13%). This study provides the first evidence for Salmonella and, more importantly, S.

enteritidis, in eggs in Trinidad. This is of major public health significance because S. enteritidis infected

eggs appear normal and the organism is difficult to detect and control. The consumption of these eggs

may increase the risk of Salmonella infection. Food safety practices, particularly the thorough cooking (>

or = 70 degrees C) of all egg dishes and the refrigeration (< 10 degrees C) of shell eggs and egg dishes,

are recommended.