Outline for a case study to improve the collaboration …
[?]Case Study
Salmonella in the Caribbean
Classroom version May 2006
This case study was developed by a working group led by the World Health Organization (WHO) EPR and is adapted from a case study written by Jeanette K. Stehr-Green, MD from the United States Centers for Disease Control and Prevention, which was inspired by an investigation conducted by Lisa Indar-Harrinauth, Nicholas Daniels, Parimi Prabbakar, Clive Brown, Gail Baccus-Taylor, Edward Commissiong, H. Reid, and James Hospedales from (1) the Caribbean Epidemiology Centre, Pan American Health Organization, World Health Organization, (2) the Food Technology Unit, Department of Chemical Engineering, University of the West Indies, (3) the Foodborne and Diarrheal Diseases Branch, Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, United States Centers for Disease Control and Prevention and (4) the Trinidad Public Health Laboratory, Trinidad.
Using this case study in the classroom:
We recommend that this case study be used in conjunction with the “Laboratory Skills for Epidemiologists” module, developed by the WHO. However, it can be delivered on its own, provided key lectures are presented first.
Recommended prerequisite lectures (cf. training matrix):
Lecture 3: Taking appropriate and adequate samples safely
Lecture 4: Transport, disinfection and biosafety
Lecture 7: Antibody and antigen detection
Lecture 8: Culture bacteriolology
Lecture 14: Typing methods
Lecture 16: Role of the laboratory in surveillance
Lecture 18: Interpreting laboratory test results
Time required for this case study:
4 hours
This case study does not come with a facilitator’s guide. The answers to all the questions for each section are provided as an introduction to the following section.
To conduct this case study in the classroom, we propose that it be distributed one page at a time. Participants should take turns reading it aloud, paragraph by paragraph. Reading all paragraphs aloud and in turns has two advantages: first, everyone can quickly participate and get beyond the inhibition of having her/his voice heard in a large room; second, time is given to the whole class to understand the issue and think about the answers. The participants reading the question may try to answer it if s/he can; otherwise, it can be discussed as a group. The next participant reads the next question and so on until the end of the page. After the next part/page is distributed, the next participant continues and so on until the case study is over. Once the epilogue is read, the class should re-visit the objectives, which reinforces their learning and provides an opportunity to clarify what may not have been fully understood.
Learning objectives
At the end of the case study, the participant will be able to:
1. Understand the role of the laboratory in public health surveillance;
2. Identify which samples to take and the transport media to use for the diagnosis of diarrheal diseases;
3. Provide the minimum epidemiologic information needed to ensure appropriate testing by the laboratory;
4. Identify the appropriate laboratory tests to request for the diagnosis of diarrheal diseases;
5. Understand and implement personal protective measures when collecting and preparing specimens for transportation to a laboratory;
6. Understand the key elements of quality assurance for laboratories;
7. Understand typing techniques used to study the epidemiology of salmonellosis;
8. Interpret Salmonella serotypes and phage types;
9. Identify the role of non-human samples in an investigation of salmonellosis;
10. Integrate epidemiological and laboratory data to formulate conclusions during an investigation.
Part 1. Salmonella in the Caribbean in the early 1990’s
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 (that may be bloody), nausea and sometimes vomiting. Fever is almost always present. The illness typically lasts for five to seven days and usually does not require specific treatment. In the immunocompromised host or in the case of an overwhelming infection in a normal host, Salmonella may spread to the blood stream and other body sites. In such cases, the infection 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 through the consumption of foods contaminated with animal feces. Implicated foods are typically those of animal origin, including beef, poultry, milk and eggs. However, 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.
As early as the mid-1980s, an increasing number of cases and outbreaks of diarrhea involving local and tourist populations made Salmonella a pathogen of public health concern in the Caribbean (Figure 1). 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.
Their disease surveillance system was based on notifiable disease reports from health care providers. Surveillance of most communicable diseases included both laboratory-confirmed cases and cases diagnosed based on clinician suspicion. However, the laboratory did not report cases of communicable disease directly. The local health department sent reports to the country’s Ministry of Health that forwarded them to the Caribbean Epidemiology Centre (CAREC) of the Pan American Health Organization /WHO.
Figure 1: Countries of the Caribbean and surrounding landmasses
Question 1a
How is salmonellosis diagnosed?
Question 1b
How could we improve the surveillance for salmonellosis in the Caribbean?
Discussion for Part 1
Many diseases can cause fever, diarrhea, and abdominal cramps. As a result, a diagnosis of salmonellosis is not made on the basis of symptoms alone. Because Salmonella most often reside in the gastrointestinal tract, infections are identified by isolating the organism from a patient’s stool. Stools specimens should be collected during the period of active diarrhea, as soon after onset as possible. The need to confirm the diagnosis of salmonellosis in the laboratory impacts our understanding of the occurrence of salmonellosis. For a case to be confirmed by the laboratory, the patient has to seek medical care, a specimen has to be collected while the patient is still shedding the organism and appropriate laboratory tests must be performed. Since only a fraction of patients with salmonellosis follow this course, the number of laboratory-confirmed cases of salmonellosis always underestimates the actual number of Salmonella infections in the community.
The described surveillance system in the Caribbean does not involve the laboratory, which is unfortunate for a disease which requires laboratory tests for a definitive diagnosis.
Part 2. Improving salmonellosis surveillance
Following CAREC’s evaluation of the Caribbean communicable disease surveillance system, a number of changes were made in the early 1990’s. These changes included:
1. Requiring laboratory confirmation for clinicians to report salmonellosis;
2. Requiring clinical laboratories to report notifiable diseases directly to the reporting authority (laboratory-based surveillance);
3. Requiring clinical laboratories to submit Salmonella isolates to the national reference public health laboratory in Trinidad for subtyping.
In the effort of improving surveillance activities, public health officials are formulating recommendations and preparing training material for the practical implementation of this improved surveillance system.
Question 2a
Which patients should submit clinical specimens for microbiological testing to detect Salmonella infection?
Question 2b
What exclusion criteria should be used when identifying such patients for microbiological tests?
Question 2c
What kind of clinical specimens should be sent to the laboratory?
Question 2d
What infection control measures should be in place for the collection of the samples?
Question 2e
What is a transport medium? When should it be used? What kind of transport media should be used to take stool specimens in this case?
Question 2f
What is a cold chain? When is there a need for a cold chain for the transport of specimen?
Discussion for Part 2
The new guidelines for Salmonella surveillance in the Caribbean recommend that all patients meeting the clinical case definition for salmonellosis submit specimens for laboratory confirmation[?]
The guidelines also point out that stool samples are better than rectal swabs for the diagnosis of salmonellosis and that specimens be collected from patients who have not received antibiotics [?]
Collecting stool samples requires use of gloves and apron as well as hand hygiene before and after the procedure. Care must me taken to avoid cross contamination between samples during collection and handling.
A transport medium (e.g., Cary Blair transport medium) is a substance in which samples are transported when it is expected that the samples will take more than 24 hours to reach the laboratory. There are different types of transport medium depending on the pathogen. The transport medium is used to maintain the viability of the potential pathogen. For some pathogens it is better not to use transport medium (or a special one designed for that pathogen) as their growth may be inhibited; this should be discussed with the laboratory receiving the specimen. Exceptions include the transport of cerebrospinal fluid taken for suspicion of bacterial meningitis, blood culture for most bacterial pathogens and stool in Cary Blair medium.
Cold chain is generally needed for all laboratory specimens, including stool samples for bacterial culture, with few exceptions.[?]
Part 3. Designing the improved surveillance system
In creating the guidelines for the reporting system, it is important to address communication needs and expectations among the players (lab, epi and others) within the surveillance network.
Question 3a
What kind of information should be made available to the laboratory with each sample to ensure appropriate laboratory testing?
Question 3b
What steps should be taken to ensure the system runs as planned? What kind of contact should be made with the laboratory prior to sending samples?
Question 3c
What laboratory test will be used to diagnose Salmonella infection?
Discussion for Part 3
With each stool sample submitted, the clinician should send a form with the following information on the patient sampled:
1. Type of sample
2. Name, patient ID number (e.g., assigned outbreak number, if related to an outbreak)[?]
3. Address
4. Date of onset of symptoms
5. Signs and symptoms of the patient
6. Date of collection
7. Prior antibiotic treatment if any (which ideally should be none for all samples)
In setting up this new surveillance network, operation manuals and standard operating procedures were distributed to all institutions involved in the new surveillance system, including clinicians and clinical laboratories. Training sessions were organized.
In order to optimize the functionality of the system, clinicians are encouraged to establish a good working relationship with their clinical laboratory - this could be done by identifying a corresponding microbiologist (make note of his name, title, phone number and e-mail address). When you are ready to send a sample, a call should be made to the laboratory beforehand, to confirm that the laboratory is ready to accept them and that there are no logistical obstacles (e.g., absence of staff during or just before a week end, increased workload due to other outbreaks). At this time, the team should clarify to whom, how and when laboratory results will be reported.
Part 4. Sending Salmonella cultures to the reference centre
Stool samples of a patient with diarrhea are cultured for enteropathogens (Figure 2, Page 7). Salmonella, Shigella, E. coli and Vibrio cholerae (and others) can all be identified in a basic laboratory using standard laboratory protocols.
Potential bacteria to look for include:
▪ Vibrio cholerae;
▪ Salmonella spp, Salmonella typhi and paratyphi; [?]
▪ Shigella;
▪ Enteropathogenic E. Coli;
▪ Campylobacter;
▪ Yersinia;
▪ Clostridium. [?]
Figure 2: Flow chart for processing diarrheal disease stool samples in a laboratory
[pic]
The proposed new surveillance system creates a network between clinical and public health laboratories. The clinical laboratories will send their isolates to the regional reference centre, the Central Public Health Laboratory in Trinidad.
The formation of this network raises issues of quality assurance and transport of isolates.
Question 4a
What is laboratory quality assurance and why is it important?
Question 4b
What are the measures that a laboratory can take to improve the quality of the results and improve its reliability?
Question 4c
Can an epidemiologist or a clinician assess the quality of a laboratory?
Question 4d
What kind of package is necessary to transport Salmonella from a clinical laboratory to the reference centre?
Question 4e
How should these samples be transported to the laboratory?
Discussion for Part 4
Laboratory quality assurance refers to a certified, and in some cases, legislated, process which aims to ensure the accuracy and reliability of laboratory services and test results, by monitoring and evaluating medical test sites for compliance with minimum standards of quality. The measures that a laboratory can take for quality assurance include (1) internal quality control processes for the pre-analytical, analytical and post analytical stages and (2) external quality assurance, such as the participation in an External Quality Assurance Scheme (EQAS).
An epidemiologist or a clinician may connect with the laboratory and tactfully enquire about quality assurance measures in place. One might enquire about the type of assays and/or reagents being used, as well as ask about their sensitivity and specificity. One must take into account the reputation and track record of the laboratory, including previous collaboration (either clinical management or outbreak investigation). Having said this, an epidemiologist or a clinician is not in a position to assess the reliability of the laboratory or to evaluate its quality assurance procedures as this requires a specific expertise.
Figure 3: Transport of Salmonella isolates as per WHO/IATA recommendations [?]
The sending laboratories should follow the WHO packaging recommendations for category B specimens (Figure 1). [?]
1. The sample is placed in a primary watertight receptacle with thick walls.
2. The primary receptacle is then placed in a second watertight container (e.g., hard box made of metal or plastic) and surrounded by absorbent material (e.g., cotton). This secondary watertight container will have the specimen data form taped on its surface while another copy will be sent directly to the laboratory by fax.
3. The secondary container is placed in a hard box (e.g., wood, metal, cardboard, plastic) and surrounded by more absorbent material. This box displays the address of the laboratory and the contact information of the sender. Category B specimens do not require a biohazard label.
Part 5. Reviewing surveillance data
Among Caribbean countries, Trinidad and Tobago implemented the new surveillance system quickly because of the close proximity of CAREC and the reference laboratory. Subsequently, several large outbreaks of salmonellosis were detected and investigated, allowing appropriate control measures. However, salmonellosis continued to occur at a high rate in that country.
In 1998, the reference centre summarized the data on reported laboratory-confirmed cases of salmonellosis in Trinidad and Tobago (Table 1).
Table 1: Laboratory isolates of Salmonella by year of diagnosis, Trinidad and Tobago, 1988-1997
|Salmonella infections |Year of Diagnosis |
| |1988 |1989 |
|Ate chicken |0.5 |0.4 |
|Ate shell eggs |8.8 | ................
................
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