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Laboratory Diagnosis in Outbreak Investigations

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  1. Laboratory Diagnosis in Outbreak Investigations

  2. Goals • Provide examples of how a variety of laboratory diagnostic techniques are used in investigational outbreak settings 

  3. Ways Laboratory Results can be used in Outbreak Investigations • Laboratory diagnosis can be used to: • Identify the agent causing an outbreak • Confirm cases in an outbreak • Link cases to the same outbreak • Identify the strain or serotype of an agent involved in an outbreak • Learn more about the epidemiology of infectious agents for research purposes • Each use is illustrated using an outbreak example

  4. Identifying the Agent Causing an Outbreak • Correctly identifying the agent may allow more effective prevention.  • 1998-1999: 3 clusters of febrile encephalitis in Malaysia reported to the Malaysian Ministry of Health • Total of 200 cases, more than 100 deaths. • 9 similar cases reported in Singapore, including 1 death • Investigators initially suspected Japanese Encephalitis • JE is a viral encephalitis transmitted through the bite of a mosquito, endemic to the area • Some specimens tested positive for JE • Previously unknown virus grew when nervous system specimens cultured 

  5. Identifying the Agent Causing an Outbreak • Cases mostly adult men with swine contact • JE not usually associated with swine, so JE less plausible • Samples from 13 patients sent to CDC for testing • JE identified from only 1 specimen • Samples then examined under an electron microscope; structure of similar in shape to a paramyxovirus • Additional laboratory tests performed • Virus found to be related to Hendra virus (first identified in Hendra, Australia) • Tissues from deceased patients were antibody positive • Antibodies also found in the serum of some patients • Virus itself found in tissues of other patients

  6. Identifying the Agent Causing an Outbreak • Similar investigations performed among swine to examine epidemiologic link • Virus found in the central nervous system, lung, kidney tissues from swine at affected farms in Malaysia • Singapore cases handled swine from Malaysia • To prevent further infection: • Transport of swine within Malaysia banned • Use of personal protective measures (gloves, masks, etc.) encouraged for swine workers • Importation of swine from Malaysia prohibited by neighboring countries • Research on epidemiology and transmission of virus among swine and humans ongoing

  7. Confirming Cases in an Outbreak • December 2005: outbreak of mumps in Iowa • By May 2006, spread to (at least) 10 additional states with 2,597 reported cases • Mumps is clinically characterized by swelling of the parotid (a large salivary gland) or other salivary gland that lasts for more than 2 days and cannot be associated with another cause • 8 states (Illinois, Iowa, Kansas, Missouri, Nebraska, Pennsylvania, South Dakota, and Wisconsin) reported ongoing local transmission or case clusters • 3 states (Colorado, Minnesota, and Mississippi) reported cases related to recent travel from outbreak state • Infected individuals traveling by aircraft implicated as most likely source of transmission

  8. Confirming Cases in an Outbreak • Cases reported January 1 to May 2, 2006: • Iowa - 1,487 • Kansas - 371 • Illinois - 224 • Nebraska - 201 • Wisconsin – 176 • Of the 2,597 cases reported by 11 states: • 1,275 confirmed (a little less than half) • 915 probable • 287 suspect • 120 unknown • Why do the case numbers jump around?

  9. Confirming Cases in an Outbreak • Many investigations use several levels of a case definition • “Suspected” cases appear to have the illness • “Probable” cases have the symptoms and perhaps an epidemiologic link to other cases or the source of infection • “Confirmed” cases have a laboratory-confirmed diagnosis of the disease and meet other case criteria • Cases with negative mumps test results excluded • Cases can be confirmed using laboratory tests: • Mumps virus cultured from a patient sample • PCR to prove mumps DNA present in a clinical sample • Electron microscopy to show the virus shape • Antibody stain specific for mumps used on a tissue sample

  10. Antigen detection methods • Determining presence or absence of a particular pathogen can be accomplished through antigen detectionmethods • For more information, see FOCUS Volume 4, Issue 3: Laboratory Diagnosis: An Overview • Test for physical presence of parts of the viral or bacterial pathogen • Antigens are small parts of infectious organisms that are recognized by the immune system • Laboratory uses specially made antibodies to detect antigens just as the immune system would

  11. Linking Cases to the Same Outbreak • Listeriosis is a bacterial infection caused by Listeria monocytogenes • Bacterium found in soil and water, can be present in apparently healthy animals such as cattle • Animal products, particularly unpasteurized foods, meats, and soft cheeses, can be contaminated with Listeria • Causes fever, muscle ache, nausea, occasional serious complications • Risk of premature birth or stillbirth among pregnant women • Lab diagnostic techniques can connect cases over a wide geographic area • August 1998: cases of listeriosis reported to CDC by Connecticut, New York, Ohio, Tennessee, Massachusetts, West Virginia, Michigan, Oregon, Vermont, Georgia 

  12. Linking Cases to the Same Outbreak • Cases all had same serotype (strain) of L. monocytogenes • Isolates shared the same pattern when sub-typed using pulsed field gel electrophoresis (PFGE) or ribotyping • Pattern observed was rarely seen in human infections • Multi-state case-control study conducted by CDC and state health departments • 4-week food histories taken from cases and controls • Cases much more likely to have eaten hot dogs (odds ratio = 17.3) • Opened package of hot dogs from a case patient’s home found to be contaminated with outbreak strain of L. monocytogenes • Hot dogs and other food products voluntarily recalled

  13. Identifying Specific Strains of an Agent Involved in an Outbreak • Aseptic (viral) meningitis spread by direct contact with respiratory secretions or feces • Outbreaks caused by enteroviruses: • Echoviruses 5, 7, 9, and 30 • Coxsackieviruses B1, B4, and A9 • Enterovirus 71 • Symptoms similar to encephalitis viruses (West Nile virus, St. Louis encephalitis) • Most cases asymptomatic • Virus can become central nervous system infection with fever, headache, stiff neck, photosensitivity • Occasionally encephalitis, myopericarditis, paralysis • Reporting not required nationally; CDC maintains voluntary reporting system (NESS) • Spring 2003: 7 states reported outbreaks of aseptic meningitis

  14. Identifying Specific Strains of an Agent Involved in an Outbreak • Arizona – reported 465 cases, 4 times the number for 2002 • 76% of isolates positive for echovirus 30 (E30) • 1 (2%) positive for echovirus 9 (E9) • California – more than 1,700 cases • 55% of specimens had evidence of enterovirus by PCR or culture • Of these, 85% were E30 infections; 12% were E9 infections • Georgia – 320 cases reported March to July 2003 in Augusta, compared to 227 cases statewide for entire previous year • 24 throat and rectal swab and CSF specimens positive for E9 • Enteroviruses identified by PCR from 52 additional samples • Idaho – 38 cases, compared with 4 the previous year • E30 was identified in 2 of 4 cases investigated • South Carolina – 82 cases reported to Aiken County Health Department by May, 130 cases by end of July • E9 identified from 20 specimens in 8 different counties

  15. Identifying Specific Strains of an Agent Involved in an Outbreak • Important to determine which viruses are causing a particular disease • In every outbreak, E9 and/or E30 identified, usually by PCR • E30 involved with outbreaks in western part of the U.S. • E9 more active in the east • Enteroviruses frequently associated with aseptic meningitis outbreaks, but very little activity in the years preceding 2003 • Find cyclical pattern from trends over last few decades • During years of low E9 and E30 activity, population susceptible to these viruses (generally children born in the period) grows until large enough for an outbreak • After an outbreak, enough people have been exposed to virus and have an immune response so outbreak does not occur again until enough new people enter population

  16. Why isn’t the bug identified from ALL specimens? • Possible reasons: • Pathogens present at such low levels they cannot be detected • Ill person may have recovered by the time the specimen was taken, so there is no evidence of the infection • Pathogens do not survive trip from person to specimen container to laboratory, and DNA or RNA is in poor condition • The organism being tested was not the pathogen responsible for disease! • A particular pathogen identified in several clinical specimens from same outbreak is often enough evidence • Conclusion depends on the pathogen: • If the pathogen is extremely common in the general population, could just be coincidence that it is present in a number of ill cases • If the pathogen is rare, finding it in a number of specimens is more likely to mean that it caused the outbreak

  17. Learning More About the Epidemiology of Infectious Agents • Staphylococcus aureus is a bacterium commonly present on skin and in the nose, and can occasionally cause infection • “Staph” can infect wounds or blood • Can be treated with antibiotics such as methicillin • Serious concern is emergence of S. aureus that is resistant to the antibiotic methicillin (MRSA) • MRSA often associated with hospital infections involving direct contact • Health care worker having contact with an infected patient can transmit the disease to a previously uninfected patient • Community-acquired MRSA recently recognized: • In institutions such as daycare centers and prisons • Among specific populations such as men who have sex with men

  18. Learning More About the Epidemiology of Infectious Agents • August 2003: CDC described new mode of transmission of community-acquired MRSA occurring in several different states • Laboratory diagnostic techniques used to identify MRSA apparently transmitted among sports participants • Athletes often sought medical care but were incorrectly diagnosed, leading to further medical visits and eventually hospitalization • Transmission could occur without skin-to-skin contact

  19. Learning More About the Epidemiology of Infectious Agents • Colorado – 5 cases of MRSA reported in February 2003 among members of a fencing club and their household contacts • Confirmed case defined as a club member or a household contact with signs and symptoms of MRSA infection, such as fever, pus, swelling, or pain, and MRSA cultured from a clinical isolate • Probable case defined as person with a skin or soft tissue infection, but without clinical culture • Among 70 club members, 3 confirmed and 2 probable cases (1 case was household contact) • PFGE used to verify infection with same strain of MRSA; 2 cases had identical PFGE patterns • PFGE provides quick means of visualizing unique sequences of DNA in an organism, providing a “fingerprint” that can identify an organism or distinguish between strains of the same organism

  20. Learning More About the Epidemiology of Infectious Agents • Definitive mode of transmission not determined • Sensor wires worn under fencing uniforms shared among players and had no schedule for cleaning between uses • No common source of exposure identified outside fencing club • Protective measures recommended to club members included: • Washing after every practice and tournament • Covering abrasions • Cleaning sensor wires between uses • Consulting a healthcare professional for skin lesions

  21. Learning More About the Epidemiology of Infectious Agents • September 2000: CDC and Pennsylvania Department of Health investigated MRSA among 10 members of a college football team in Pennsylvania • 7 of the 10 cases were hospitalized • All isolates had indistinguishable PFGE patterns • Possible risk factors for infection were skin trauma due to turf burns, shaving, sharing unwashed bath towels • September 2002: 2 cases of MRSA identified among members of a college football team in Los Angeles County, California • Cases had indistinguishable PFGE patterns • Players on the team reported frequent skin trauma, said they covered wounds only half of the time • Balms and lubricants also identified as potential modes of transmission

  22. Learning More About the Epidemiology of Infectious Agents • January 2003: 2 wrestlers on a high school team with MRSA reported to the Indiana Department of Health • Isolates not available for PFGE analysis • Players had never wrestled each other; sharing items such as towels or equipment could have transmitted infection • No other common sources identified • In this series of MRSA outbreaks, PFGE verified that MRSA was being transmitted between members of the same athletic team • Isolates from infected members on a given team had indistinguishable PFGE patterns, so know infections were same strain • Findings lay groundwork for future studies on modes of transmission among team members

  23. Evaluation of Prevention Measures • Another goal of public health research: to verify that protective measures employed to prevent the spread of disease are effective • Illustrated by measures taken to curb transmission of severe acute respiratory syndrome (SARS) in Taiwan and other countries in early 2003 • Because SARS was difficult to differentiate from other respiratory illnesses and initially could not be diagnosed with standard laboratory techniques, Taiwan employed widespread use of quarantine • Majority of 131,000 people quarantined March to July 2003 were close contacts of SARS patients and travelers from countries designated by WHO as SARS-affected

  24. Evaluation of Prevention Measures • Hospital staff and patients quarantined in health care facility; others quarantined at home • Required to take their temperatures 2 to 3 times a day and report immediately if fever or respiratory symptoms occurred • Under “Level A” quarantine, could not leave house for any reason unless deemed appropriate by the health authorities • Under “Level B” quarantine, could leave to seek medical attention, exercise in an outdoor area, buy food, dispose of garbage, perform other activities if approved by health authorities • Health authorities deemed the potential prevention of additional SARS cases to be worth the personal and financial costs • How effective was quarantine in preventing cases?

  25. Types of Close Contacts Quarantined During the SARS Outbreak • Health care workers • Family members • Co-workers • Classmates and teachers • Friends • Airplane passengers within 3 rows of a case • Other passengers and drivers of public transportation vehicles when the trip lasted at least one hour • People who had contact with a person in quarantine at a facility where a SARS case occurred

  26. Evaluation of Prevention Measures • Investigators evaluated how many of persons quarantined actually developed SARS • Of 50,319 people under Level A quarantine, 112 (0.22%) diagnosed with suspected or probable SARS • Of 80,813 people under Level B quarantine, 21 (0.03%) diagnosed with suspected or probable SARS • Highest rates among health care workers, family members of SARS patients, airplane passengers seated within 3 rows of a SARS patient • The lowest rates among travelers arriving from SARS-affected countries • Assuming that each case of laboratory-confirmed SARS might have led to another cluster of cases, a very large number of cases might have been prevented by implementing the quarantine

  27. Evaluation of Prevention Measures • Epidemiologic and laboratory evaluation showed which groups were most likely to develop SARS if they had contact with a patient (health care workers and family members) • SARS rates did decrease during the quarantine, but multiple prevention measures were put into effect, so the role that quarantine played remains uncertain. • A later study in Beijing evaluated how quarantine could be made more efficient • Only persons coming into contact with actively ill SARS patients needed to be quarantined; those who had contact during the incubation period before symptoms became apparent were not at risk of developing SARS

  28. Summary • From these examples, we see how laboratory diagnostic tests can be used to: • Solve outbreak investigations • Identify agents • Investigate remaining questions about infectious diseases • Laboratory diagnostic techniques are an integral part of public health surveillance, investigation, and research • Understanding the basics of how these tests work will improve your conduct of outbreak investigations

  29. Resources • CDC-recommended case definitions can be found at • Updated information on monkeypox can be found on the CDC website:

  30. References • Centers for Disease Control and Prevention. Outbreak of Hendra-like virus – Malaysia and Singapore, 1998-1999. MMWR Morb Mort Wkly Rep. 1999;48:265-269. Available at: preview/mmwrhtml/00056866.htm. Accessed December 14, 2006. • Centers for Disease Control and Prevention. Update: multistate outbreak of mumps-United States, January 1-May 2, 2006. MMWR Morb Mort Wkly Rep. ;55:1-5. Available at: Accessed December 18, 2006. • Centers for Disease Control and Prevention. Division of Bacterial and Mycotic Diseases. Listeriosis. Available at dbmd/diseaseinfo/listeriosis_g.htm. Accessed December 14, 2006. • Centers for Disease Control and Prevention. Multistate outbreak of listeriosis – United States, 1998. MMWR Morb Mort Wkly Rep. 1998;47:1085-1086. Available at: mmwrhtml/00056024.htm. Accessed December 14, 2006.

  31. References • Centers for Disease Control and Prevention. National Center for Infectious Diseases, Respiratory and Enteric Viruses Branch. Viral (Aseptic) Meningitis. Available at: dvrd/revb/ enterovirus/ viral_meningitis.htm. Accessed December 14, 2006. •  Centers for Disease Control and Prevention. Outbreaks of aseptic meningitis associated with Echoviruses 9 and 30 and preliminary surveillance reports on enterovirus activity --- United States, 2003. MMWR Morb Mort Wkly Rep. 2003;52:761-764. Available at: mmwrhtml/mm5232a1.htm. Accessed December 14, 2006. • Centers for Disease Control and Prevention. Information about MRSA for Healthcare Personnel. Available at: dhqp/ar_mrsa_healthcareFS.html. Accessed December 15, 2006.

  32. References • Centers for Disease Control and Prevention. Methicillin-resistant Staphylococcus aureus infections among competitive sports participants – Colorado, Indiana, Pennsylvania, and Los Angeles County, 2002-2003. MMWR Morb Mort Wkly Rep. 2003;52:793-795.Available at: mm5233a4.htm. Accessed December 15, 2006. • Centers for Disease Control and Prevention. Use of quarantine to prevent severe acute respiratory syndrome – Taiwan, 2003. MMWR Morb Mort Wkly Rep. 2003;52:680-683. Available at: Accessed December 15, 2006. • Centers for Disease Control and Prevention. Efficiency of quarantine during an epidemic of severe acute respiratory syndrome – Beijing, China, 2003. MMWR Morb Mort Wkly Rep. 2003;52:1037-1040. Available at: mm5243a2.htm. Accessed December 15, 2006.