WRAP-UP - OUTBREAK OF AN INFLUENZA-LIKE ILLNESS AMONG PIG FARMERS IN MALAYSIA

1. WRAP-UP - OUTBREAK OF AN INFLUENZA-LIKE ILLNESS AMONG PIG FARMERS IN MALAYSIA

2. Question 1: Briefly describe the outbreak in terms of person, place, and time. Also, provide a working case definition for the illness. Answer: • Person: People between the ages of 13 to 68, mostly of Chinese ethnicity, predominantly male, and most had occupations involving direct contact with pigs. • Place: Pig-farming villages of Malaysia. • Time: The outbreak occurred between September and June. The information on the 94 patients is from a four month period during this outbreak.

3. Question 1: Briefly describe the outbreak in terms of person, place, and time. Also, provide a working case definition for the illness. Answer: Possible case definition: People who live or work in pig-farming villages who presented with an influenza-like illness (fever, headache, dizziness, vomiting, reduced level of consciousness, nonproductive cough, myalgia, impaired focal neurologic signs) between September and June. We may wish to extend the time period beyond September and June to find both early and late cases.

4. Question 2: Using an appropriate measure, calculate which symptoms appear most important in this outbreak? Answer:from Table 1, symptoms of patients

5. Percentage of symptoms of patients Fever, headache, and dizziness appear to be the most important symptoms in this outbreak.

6. Question 3:Outbreaks of influenza-like illnesses have assumed new importance with concern about avian influenza (“bird flu”). If you were investigating this outbreak today, would you have to worry about the possibility that this was avian influenza? Answer: • Symptom/illness experienced by the cases are influenza-like; • There is not enough information suggesting the presence of infected domestic poultry associated with avian influenza • Pigs are susceptible to infection from both avian and mammalian viruses, resulting in the emergence of a novel subtype or antigenic shift; • The level of awareness and caution should always be raised

7. Question 4:What clues should have alerted the officials that JE virus might not have been the agent at work? Answer: • Person: epidemiologic characteristics of this outbreak are different from an outbreak of JE virus • Most of the cases were in men (77/94=81.2%) who worked with pigs in some capacity (87/94=92.6%) • Very few case patients were young children (mean age: 37 years) • JE virus outbreaks both men and women are affected, there is no association with one particular occupation, and children are the group most commonly infected. • Thus, JE virus is not the likely agent in this outbreak.

8. Question 5: a) Which one of these organisms do you think is responsible for the outbreak? b) What are your proposed reservoir, source, and mode of transmission?. Answer: • Based on the clinical data and the information on person, place, and time, Nipah virus is the infectious agent involved in this outbreak. • The likely reservoir is fruit bats, the source is infected pigs, and the mode of acquisition is animal-to-person with people becoming infected via direct contact with contaminated tissues or body fluids of infected pigs.

9. Question 5: b) What are your proposed reservoir, source, and mode of transmission?. Answer: • Mode of transmission from animal to human is uncertain • In Malaysia, transmission appeared to require close contact with contaminated tissue or body fluids from infected animals • Spread to individuals at a distance were rare • Indirectly suggests that true airborne spread beyond the immediate vicinity of a victim is unlikely • Spread from contaminated tissue or body fluid by droplets that are inhaled remains a possible source of the infection.

10. Question 6: What control measures now should be implemented in this region of Malaysia? Briefly explain your choices. Answer: • Possible control measures would include • Isolating or slaughtering infected pigs • Urging people who work with pigs to avoid the body fluids of these animals by wearing protective clothing, boots, gloves, gowns, goggles, and face shields • Encouraging pig farm workers to wash their hands and other possibly contaminated objects on a regular basis • Educating the public on the signs and symptoms of Nipah virus not only in people, but also in pigs.

11. Question 6: What control measures now should be implemented in this region of Malaysia? Briefly explain your choices. Answer: In fact, officials in Malaysia enacted these control measures • Health education and health advice to people working in pig farms was given through news media and electronic media such as radio and television. • Health care workers strictly adhered to universal precautions in the management of severely ill patients • Personal protection; using masks, goggles, gowns, and boots was advocated • Hand-washing after handling of infected animals and pigsties, and cages and vehicles for transporting animals were washed down with soap and water

12. Question 6: What control measures now should be implemented in this region of Malaysia? Answer: • A 2-phase pig-culling operation was conducted that included all infected pig farms in the outbreak areas • Phase-I involved culling in areas where outbreak cases occurred. More than 1 million pigs were culled. • Phase-II involved surveillance in all pig farms throughout the country • This process was carried out for 3 months; farms at which >3 samples had positive results of testing for Nipah virus were considered to be positive farms, and all pigs at the affected farms and at farms within a 500m radius were culled

13. POINTS FROM PROBLEM I. Outbreak Investigation • This case illustrates the importance of a quick response effort to determine: • The unknown agent(s) causing illness • Appropriate control measures to contain disease • Suitable surveillance systems that can detect future outbreaks at earlier stages • Verify diagnosis - This case provides an example of the need for rapid verification of the agent • The importance of collection of specimens for laboratory testing to confirm diagnosis, particularly for viral respiratory illnesses with similar symptoms

14. POINTS FROM PROBLEM II Nipah virus was a newly recognized disease, very little was known about it. Some possibilities: • You might want to collect more information on the pigs and attempt to figure out how they are becoming infected. • Are all pigs infected? • Which pigs do not become infected? • Is there a particular tree that fruit bats like that is planted around these pig-farming villages? • Are the fruit bats contaminating the food supply of the pigs with their secretions?

15. POINTS FROM PROBLEM II Nipah virus was a newly recognized disease, very little was known about it. Some possibilities: • Is there a way to test pigs to see if they have become infected? • To collect specimens from ill/dead pigs and get information from the farmers about the layouts of their farms, the prevalence of fruit bats in the area, the trees planted on the farms, etc. • To identify risk factors for disease, only cases were in the study, no comparison group. You could attempt to find controls (perhaps other people who worked on these farms but did not become infected) • Interviews with cases and controls to find out which features or characteristics put someone at an increased risk of becoming infected with Nipah virus.

16. POINTS FROM PROBLEM II Nipah virus was a newly recognized disease, very little was known about it. Some possibilities: • You might want to find out why Nipah virus is emerging now. • Has it always been around? • Are there any stored samples of blood that you can test for the presence of Nipah virus? • Has something happened with the climate that is increasing the prevalence of fruit bats? • Or has industrialization driven the fruit bats out of their normal habitats and forced them into new areas?