Download Injury Epidemiology, Prevention and Control

EPIDEMIOLOGY
Outbreak Investigation
Sue Lindsay, Ph.D., MSW, MPH
Division of Epidemiology and Biostatistics
Institute for Public Health
San Diego State University
US Public Health Service Commissioned Corps
http://www.usphs.gov/
Citizen Emergency Response Teams
http://www.citizencorps.gov/cert/
The Natural History of Disease
Healthy
Disease Symptoms Seek
Onset
Care
Outcome
Diagnosis/
Treatment
Pre-Clinical Disease
• Incubation Period
• Latency Period
Incubation Period
• The period of time from exposure
to infectious agent to the onset of
detectable clinical illness
Factors that Affect
Incubation Period
• Invasive ability of the infectious agent
• The time needed for replication and growth
of the infectious organism until clinical
disease is achieved and manifested
• The body site of infection
• Dose
The Epidemiologic Curve
• The distribution of number of new
cases of a disease by date or time
of onset
Number of People
Incubation Period For 191 Infected by
Salmonella Outbreak, Wales, 1986
Salmonella Outbreak, Wales,
1986
• Characterized by a
rapid, explosive rise in
the number of cases in
first 16 hrs.
• This curve suggests a
common-source,
single-exposure
epidemic
Number of People
What does this pattern suggest?
Chronic Disease:
Latency Period
• The analog for incubation period in noninfectious diseases is the latency period
• Example: The period of time from
exposure to a carcinogen to the onset of
cancer.
Incidence Rate Per 100,000
Annual Incidence Rate of Leukemia After
Atomic Bomb Explosion
Hiroshima, Japan, 1945-1957
Number of Cases
281 Cases of Bladder Tumors
Among Dyestuff Workers
Emerging Infectious Diseases
“To write about infectious diseases is almost to write
of something that has passed into history. The most
likely forecast about the future of infectious disease, is
that it will be very dull”
Natural History of Infectious Disease, 1962
Emerging Infectious Diseases
• Since 1975, previously unknown diseases have surfaced at an
alarming pace, more than 30 new diseases in 30 years, most of
them newly discovered viruses.
• These new viruses tend to come from other species – zoonosis
• Ebola, HIV, avian influenza
• Viruses are “masters of interspecies navigation”
What is Going On?
• Archeological evidence suggests that small, nomadic
human groups hardly every suffered from contagious
disease.
• Agriculture and the domestication of animals brought
humans into close exposure to animals, animal and
human waste, and reservoirs of disease.
Human Disease from Animals
•
•
•
•
•
•
•
Tuberculosis
Measles
Smallpox
Whooping cough
Typhoid fever
Influenza
Leprosy
goats
cows
cattle
pigs
chickens
ducks
water buffalo
• Common cold
horses or cattle
• Peptic ulcer (helicobacter)
sheep’s milk
What is Going On?
• The chief risk factor for emerging zoonotic diseases is
environmental degradation by humans.
World Health Organization Coordinator for Zoonoses Control
• Global Climate Change
• Deforestation/Infringement on animal habitat
• Industrialization and intensification of the animal production
sector (intensive factory farming)
Avian Influenza
• Natural reservoir is wild ducks
• Causes epidemics in poultry and other bird populations exposed to
infected ducks
• Requires dense populations of birds, unsanitary and stressful
conditions
• There has been a significant increase in bird flu epidemics with the
advent of high density indoor poultry farming and the globalization
of this type of poultry production
• Most avian influenza strains do not generally jump from birds to
humans
Avian Influenza
• RNA virus with two types of enzyme spikes protruding from the
surface of the virus, causing illness in birds
• 16 hemagglutinin enzymes (H1 to H16)
• 9 neuraminidase enzymes (N1 to N9)
Pandemic human infections began:
• 1918 Flu:
H1N1, killed 100 million people “Spanish flu”
• 1957 Flu:
H2N2, killed 1 million people worldwide “Asian flu”
• 1968 Flu:
H3N2, 40% US adolescents sick “Hong Kong flu”
• Current H5N1 started in humans in 1997 in China…
Avian Influenza H5N1
• Spring 1997 in Hong Kong: thousands of chickens were dying from
H5N1
• May 14 1997 Hong Kong: 3 year old boy died of multiple organ
failure: H5N1
• 18 sick, 6 died in Hong Kong in 1997: all multiple organ failure, all
had been exposed to chickens
• Hong Kong ordered the slaughter of more than a million birds
• Human infections ceased
Avian Influenza H5N1
• Early 2004: Widespread outbreaks of H5N1 in chicken flocks
throughout eight countries in Southeast Asia with evidence that the
virus was mutating to more virulent strains
• December 2006, 263 laboratory confirmed human cases, 158 deaths
in ten countries (60% mortality). Two cases of very close contact
human-to-human transmission. No evidence of airborne human-tohuman transmission.
• December 2007, 351 laboratory confirmed human cases, 217 deaths
in twelve countries (62% mortality)
• June 2008, 385 laboratory confirmed human cases, 243 deaths in
twelve countries (63% mortality)
• August 2009, 438 laboratory confirmed human cases, 262 deaths in
twelve countries (60% mortality)
Avian Influenza H5N1
• H5N1 has infected other mammals:
• Pigs
• Cats
• Tigers
• Leopards (more than 100 big cats at a Thailand zoo)
• Ferrets.
• These home and zoo outbreaks suggest viral infection in the meat
of chicken used as feed.
Avian Influenza H5N1 - 2006
• “Recent laboratory and epidemiologic studies have yielded
disturbing evidence that the H5N1 virus has become progressively
more pathogenic in poultry, has increased environmental
resistance, and is expanding its mammalian host range”
New England Journal of Medicine
• “The virus remains unstable, unpredictable and very versatile.
Anything could happen. Judging from the way the virus has
behaved, it may have new and unpleasant surprises in store for us”
World Health Organization
• “H5N1 is the one that scares us shitless”
Robert Webster, Chair of Virology, St Jude
Children’s Research Hospital
H5N1 Epidemiologic Curve: August 11, 2009
Total = 438 cases, 262 deaths (60%)
China
Vietnam
Thailand
Vietnam
Cambodia
Indonesia
China
Thailand
Vietnam
Azerbaijan
Cambodia
China
Indonesia
Djibouti, Iraq,
Turkey, Egypt
Thailand
Bangladesh
Cambodia
China
China
Egypt
Indonesia
Djibouti, Egypt, Iraq, Indonesia
Vietnam
Turkey
Thailand, Vietnam Cambodia
Lao, Myanmar
Nigeria, Pakistan
China
Egypt
Indonesia
Vietnam
H5N1 in Poultry and Wild Birds
December 7, 2007
Human Cases of Avian H5N1
As of May 6, 2009
Swine Influenza
• Natural reservoir is swine (pigs)
• Causes epidemics in pigs and are a challenge to the swine industry
• Swine have both avian and mammalian receptors, allowing viruses
to exchange genetic material and produce new virus - “mixing
vessels”. Swine flu is frequently found in farmed turkeys.
• Most outbreaks in swine herds occur in the fall and winter
• Swine flu in European herds differ genetically from North American
Swine flu infections in herds.
• Most swine influenza strains do not generally jump from swine to
humans, very rarely human infections
Swine Influenza
In Swine
• A (H1N1) – 80 years in swine herds, very stable
• 1998 – H3N2 emerged in US swine. Contained avian, human,
and swine viral genes
• Also H1N2 and H3N1 exists in swine herds
Human infections:
• 1976 Flu:
Soldiers in Fort Dix, New Jersey, 1 death. The virus
circulated for one month and then disappeared.
• Current H1N1 started in humans this year in North America
Novel A (H1N1)
• Contains human, avian, and swine genes. It has NEVER been
identified in a swine herd. Can it be called swine?
• Contains gene segments from both European and North American
swine genotypes.
• Human-to-human transmission with no proof of swine-person
transmission.
• Morbidity is high and mortality is low compared to H5N1 avian
influenza
Novel H1N1 Genotype
http://id.uga.edu/docs/swine-flu-summary-genotype.pdf
Novel H1N1 Influenza
Mexico
• March 15, 2009. Infection in a young boy in Veracruz, Mexico
• March 17, 2009. Infection in Oaxaca, Mexico
• Between March 18th and April 18th, 47 cases
California
• March 28, 2009. Infection in a young girl in Brawley, California
• Younger sibling sick 10 days earlier
• No exposure to pigs/swine, travel to Mexico, or exposure to
Mexican travelers
• CDC unable to type
Veracruz, Mexico
March 15th, 2009
Oaxaca, Mexico
March 17th, 2009
Brawley, California
March 28th, 2009
Novel H1N1 Epidemiologic Curve: August 23, 2009
Total = 209,438+ cases, 2185+ deaths (1%)
11 countries
51 countries
120 countries
Africa
Americas
Eastern Med
Europe
Southeast Asia
Western Pacific
Africa
Americas
Eastern Med
Europe
Southeast Asia
Western Pacific
Novel H1N1 World Spread
http://gamapserver.who.int/h1n1/cases-deaths/h1n1_casesdeaths.html
Considerations for Pandemic Influenza
1.
Pandemic influenza can have different origins (avian, swine)
2.
Influenza pandemics are recurring events
3.
The world is experiencing a new pandemic
4.
Do we have adequate supplies of antiviral medicine and vaccines?
5.
Humans have no immunity – widespread illness
6.
Economic and social disruptions could be great
Mitigation
You need a balance between:
• Reducing illness and death through social
distancing
• Minimizing social disruption
• Interventions shouldn’t be worse than the
disease!
Steps in the Investigation of an
Acute Disease Outbreak
I. Define The Epidemic
• Identify cases
• Clinical features
• Is this a known disease?
• Serology/Cultures
• Cause Understood?
II. Examine Time and Place
• Who is getting the
disease? Specific
populations?
• Plot onset times and
number of cases
• Look for relationships
between time and place
• Collect lots of information!
• If exposure known,
calculate attack rates
III. Develop Hypotheses
• Use existing knowledge
• Analogy to diseases of
known etiology
IV. Test Hypotheses
• Further analyze
existing data
• Collect more data
V. Recommend Control Measures
• Control of present
outbreak
• Prevention of future
outbreaks
Etiologic Investigation of a
Food-Borne Outbreak
• May 23, 1996, Charleston, South Carolina
• Luncheon – 64 attendees
• 39 persons developed diarrheal illness
• What is the overall attack rate?
• 39/64 = 61%
Etiologic Investigation of a
Food-Borne Outbreak
Ate Sick
AR
Not eat Sick
Ham
25
11
44%
37
26
70% 0.6
P. Salad
19
16
84%
42
20
48% 1.8
Raspberries
37
33
89%
24
4
17% 5.2
Overall attack rate 61%
AR
RR
Homework
Chapter 2, page 35, Questions 2&3
Due September 25, 2009
Ate Sick
AR
Not eat Sick
AR
Ate egg salad
___ ___
____
____
____ ___
Ate tuna
___ ___
____
____
_____ ___
Ate both
___ ___
____
____
_____ ___
Use the information from the two tables in your text to populate this table and answer
the two questions. For full credit on your homework, we will need to see this table!