Sampling in outbreak investigation

Editor's Notes

• #2: No matter what you wear when you collect specimens, this is one of the first and most important steps in an outbreak investigation. Laboratory results are extremely valuable, as they can help identify the causative agent, provide information about the mode of transmission and identify possible outbreak sources. Clinical, demographic and risk factor information from an outbreak investigation can also provide important clues about the cause(s) of an outbreak (and steps to control it). Since time can be lost waiting for laboratory results, collection and processing of outbreak-associated specimens usually occur simultaneously with other outbreak investigation steps, such as epidemiologic data collection and hypothesis generation. Using examples from real outbreak investigations, this issue of FOCUS discusses some of the different types of specimen collection that may be required during an outbreak. While we review each type of specimen separately for the sake of clarity, more than one type of specimen is often collected in a real outbreak investigation. We will also discuss some of the practical issues of clinical specimen collection, including packaging, shipping, and other logistical issues.  
• #3: Many outbreak investigations involve the collection of human clinical specimens from outbreak-associated case-patients. Human clinical specimens include blood, serum, urine, saliva, hair, feces, etc. The type of specimen collected depends on the nature of the outbreak. For example, stool specimens may be collected during an outbreak of diarrheal illness, while blood may be collected during an outbreak of fever and rash suggestive of rubella. Similar specimens can also be taken from animals when investigators suspect that they may be involved in an outbreak.  
• #4: A final challenge in detecting infectious agents in the environment has to do with the time sensitivity of specimen collection. To ensure sample integrity and proper diagnosis and treatment, specimens need to be collected as quickly as possible once an outbreak is suspected. For instance, in a foodborne disease outbreak, the implicated food may be discarded or consumed in a matter of days.  
• #5: Typically, most specimen collection that occurs during a disease outbreak involves human clinical specimens. Here we will touch upon some important issues in planning, collecting, processing, labeling, storing, and transporting human clinical specimens. Laboratory confirmation of an etiologic agent is a critical component of a successful outbreak investigation. For this reason, it is important to remember that the ability of a laboratory to successfully identify a pathogen depends on appropriate specimen collection and transportation (10).  
• #6: When a suspected outbreak is first reported, the clinical and epidemiological data collected should be used to narrow the range of possible causative agents. Once this is done, the clinical specimens needed to make a laboratory-confirmed diagnosis should be determined. Next, a laboratory must be selected to perform the testing and analysis. This may be determined in part by the test(s) needed. Routine laboratory tests, such as those used for the detection of Salmonella species, can be performed by most clinical laboratories. However, the laboratory capability to test for agents such as Clostridium botulinum toxin is more limited.  
• #7: Because each laboratory has its own specific guidelines for specimen collection, all aspects of the specimen collection process (including the sample type, materials needed, local or on-site processing, transportation, and communication of results) should be discussed with the laboratory before specimen collection begins.
• #8: Transportation details such as the timing and delivery of the collected samples, required transport media, transit route, shipping requirements, temperature requirements, and documentation (i.e., chain of custody forms—see FOCUS Volume 2, Issue 6 for more information) should also be discussed. Packaging and transportation requirements must comply with national regulations for transporting infectious material and should also be reviewed with the transport service.   
• #9: Specimens should be collected as soon as possible once an outbreak has been identified. Human specimens obtained early, particularly before antimicrobials are given to the patient, are more likely to yield the pathogen. In certain situations, however, specimen collection after a person recovers from illness may be equally important, because the presence of antibodies in serum samples after recovery can confirm whether or not an individual’s illness or infection was in fact related to the outbreak in question.
• #10: Before obtaining human clinical specimens, it is important to explain the purpose and procedure to the case-patient. The investigator must obtain an adequate amount of the specimen and handle it with care, because this may be the only opportunity to obtain a specimen during the outbreak. A sample must be collected properly in order to ensure that the pathogen or infectious agent can be recovered in a viable form.  
• #11: Before obtaining human clinical specimens, it is important to explain the purpose and procedure to the case-patient. The investigator must obtain an adequate amount of the specimen and handle it with care, because this may be the only opportunity to obtain a specimen during the outbreak. A sample must be collected properly in order to ensure that the pathogen or infectious agent can be recovered in a viable form. Appropriate specimen collection technique is also important because the laboratory may otherwise reject the specimen. For example, if there is an insufficient sample quantity or contamination from other body fluids, the laboratory may not be able to process the specimen (10).  
• #12: Over 70% of the information used by a clinician to diagnose and treat a patient is derived from laboratory testing. Thus, ensuring that specimens are accurately labeled at collection time is essential. Misidentification of a specimen leads to misidentification of a patient, which can result in improper diagnosis and treatment (11).
• #13: Over 70% of the information used by a clinician to diagnose and treat a patient is derived from laboratory testing. Thus, ensuring that specimens are accurately labeled at collection time is essential. Misidentification of a specimen leads to misidentification of a patient, which can result in improper diagnosis and treatment (11).
• #14: A case investigation form with matching information should be completed for each specimen at the time of specimen collection and retained by the investigation team for reference. And, of course, all of the above information should be printed legibly
• #15: Specimens must be stored appropriately before and during transportation in order to preserve the integrity of the specimen. Since microorganisms are living beings, environmental conditions can affect their maintenance and survival. If they multiply or die during collection, transport, or storage, they no longer accurately represent the disease process in the person from whom the specimen was taken (10). For this reason, storage in an appropriate medium and maintenance of the proper temperature is critical.
• #16: Requirements depend on the type of specimen and sample and should be determined in consultation with the laboratory before specimen collection begins. Most specimens (with the exception of feces) need to be transported in sterile containers (10). Specimens transported in incorrect containers (i.e., a non-sterile container when sterility is required) may be rejected by the laboratory. All specimen containers should be closed tightly. Laboratories may reject a specimen if it shows signs of leakage or seepage, since this could potentially expose laboratory personnel to the contents (10).  
• #17: Packaging of clinical specimens must comply with postal and commercial regulations for transport of infectious materials. These regulations depend on the type of transport (i.e., ground or air delivery) and should be determined in consultation with the laboratory and carrier prior to specimen collection. Finally, the receiving laboratory should be notified of the pending shipment before transport.  
• #18: This issue has touched upon the ways in which clinical and environmental specimens can provide valuable information to an outbreak investigation, and the importance of appropriate and timely specimen collection. The next few issues of FOCUS will discuss in more detail what happens after a specimen is collected and sent to the laboratory and what types of laboratory diagnostics may be used to help identify an agent suspected in an outbreak
• #19: Additional resources for specimen collection include the World Health Organization’s “Guidelines for the collection of clinical specimens during field investigations of outbreaks, 2000” and the CDC’s “Guidelines for specimen collection.” State health department websites often have information on specimen collection; searching the appropriate state health department website for this information may be useful