Điều tra vụ bùng phát bệnh từ thực phẩm - Lê Hoàng Ninh

Điều Tra Vụ bùng phát 
bệnh từ thực phẩm 
GS, Ts Lê Hoàng Ninh 
Epidemiology (Schneider) 
Bùng phát là gì ?(outbreak) 
Dịch ( epidemic) hay còn gọi là bùng phát ( outbreak)khi 
số ca bệnh cao hơn số dự kiến xảy ra ( trị số bình 
thường) tại một địa phương, khu vực nào đó, hay trên 
một nhóm dân số nào đó trong một thời khoảng nhất 
định 
Epidemiology (Schneider) 
Bệnh lưu hành địa phương 
(endemic)và dịch ( epidemic) 
Lưu hành Dịch 
S
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 b
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Thời 
gian 
Epidemiology (Schneider) 
Tại sao phải điều tra bùng phát/ dịch? 
 Kiểm soát và phòng ngừa 
 Sự ác tính và nguy cơ lây truyền cho người khác 
 Cơ hội nghiên cứu để hiểu biết tốt hơn 
 Cơ hội đào tạo 
 Xem xét chương trình y tế 
 Cab quan ngại khác: luật, chính trị, công cộng 
Epidemiology (Schneider) 
Step 1: Verify the outbreak 
 Determine whether there is an outbreak – an 
excess number of cases from what would be 
expected 
 Establish a case definition 
 Non-ambiguous 
 Clinical / diagnostic verification 
 Person / place / time descriptions 
 Identify and count cases of illness 
Epidemiology (Schneider) 
Step 2: Plot an Epidemic Curve 
 Graph of the number of cases (y-axis) by their date or 
time of onset (x-axis) 
 Interpreting an epidemic curve 
 Overall pattern: increase, peak, decrease 
 Type of epidemic? 
 Incubation period? 
 Outliers: 
 Unrelated? 
 Early or late exposure? 
 Index case? Secondary cases? 
• Starts slowly 
• Time between the first case and the peak is comparable 
to the incubation period. 
• Slow tail 
Vector-borne Disease 
• This is the most common form of transmission in food-
borne disease, in which a large population is exposed for 
a short period of time. 
Point Source Transmission 
• In this case, there are several peaks, and the incubation 
period cannot be identified. 
Continuing Common Source or Intermittent Exposure 
Salmonellosis in passengers on a flight from London 
to the United States, 
by time of onset, March 13--14, 1984 
Source: Investigating an Outbreak, CDC 
Legionnaires' Disease 
By date of onset, Philadelphia, July 1-August 18, 1976 
Source: Investigating an Outbreak, CDC 
Foodborne Outbreak (Propagated) 
Source: CDC, unpublished data, 1978 
Epidemiology (Schneider) 
Step 3: Calculate attack rates 
Attack rate = (ill / ill + well) x 100 during a time period 
If there is an obvious commonality for the outbreak, calculate 
attack rates based on exposure status (a community picnic) 
If there is no obvious commonality for the outbreak, calculate 
attack rates based on specific demographic variables 
(hepatitis cases in a community) 
Epidemiology (Schneider) 
Step 4: Determine the source of the epidemic 
If there is an obvious commonality for the 
outbreak, identify the most likely cause and 
investigate the source to prevent future 
outbreaks 
If there is no obvious commonality for the 
outbreak, plot the geographic distribution of 
cases by residence/ work/school/location and 
seek common exposures 
Epidemiology (Schneider) 
 Control of present outbreak 
 Prevention of future similar outbreaks 
Step 5: Recommend control measures 
The vast majority of outbreaks 
are food-borne 
Foodborne Disease Outbreak 
 An incident in which (1) two or more persons experience 
a similar illness after ingestion of a common food, and 
(2) epidemiologic analysis implicates the food as the 
source of the illness 
Intoxication – ingestion of foods with 
Toxicants found in tissues of certain plants (Jimpson Weed) 
and animals (seal liver) 
Metabolic products (toxins) formed and excreted by 
microorganisms while they multiply (botulinum toxin) 
Poisonous substances introduced during production, 
processing, transportation or storage (chemicals, pesticides) 
Foodborne Disease Outbreak (cont.) 
 Infections – Caused by the entrance of pathogenic 
microorganisms into the body and the reaction of the 
body tissues to their presence or to toxins they 
generate within the body 
 Rule of thumb – but not law 
Intoxicants are rapid onset, no fever 
Toxins in the stomach produce vomiting 
Toxins in the intestines produce diarrhea 
Infections produce fever 
Epidemiology (Schneider) 
Types of Foodborne Contamination 
 Physical 
 Glass, metal fragments, tacks, dirt, bone, etc. 
 Chemical 
 Pesticides, cleaning compounds, poisonous 
metals, additives and preservatives 
 Biological 
 Bacteria, viruses, fungi, yeast, molds, parasites, 
poisonous fish and plants, insect and rodents 
Epidemiology (Schneider) 
Bacterial Requirements 
 Food: Most bacteria require what is known as 
potentially hazardous food 
 Milk or milk products, eggs, meat, poultry, fish, 
shellfish, crustaceans, raw seed sprouts, heat 
treated vegetables and vegetable products (fruits?) 
 Generally high protein, moist foods 
Epidemiology (Schneider) 
Bacterial Requirements (cont.) 
 Water: Bacteria require moisture to thrive 
 The water activity (Aw) is the amount of water 
available in food 
 The lowest Aw at which bacteria will grow is 0.85 
 Most potentially hazardous foods have a water activity of 
0.97 to 0.99 
 pH: Best growth at neutral or slightly acidic pH 
 Potentially hazardous foods have a pH of 4.6 – 7.0 
Epidemiology (Schneider) 
Bacterial Requirements (cont.) 
 Temperature: The danger zone for potentially 
hazardous foods is 45 to 140 degrees Fahrenheit 
 This is the zone where most bacterial growth 
occurs 
 Time: Potentially hazardous foods must not be 
allowed to remain in the danger zone for more than 
4 hours 
 Oxygen: Some bacteria require oxygen while 
others are anaerobic and others are facultative 
Epidemiology (Schneider) 
 Improper cooling of foods 
 Improper cooking of foods 
 Improper reheating of foods 
 Improper holding temperature of foods 
 Cross contamination 
 Infected food handlers, poor employee hygiene 
Major Causes of Foodborne Disease 
Temperature and Bacteria Control 
250 
240 
Canning temperatures for low-acid vegetables, meat, and poultry in pressure canner 
212 
125 
120 
- 20 
165 
140 
98.6 
60 
45 
32 
0 
0 F 
Some bacterial growth; many bacteria survive 
Canning temperatures for fruits, tomatoes, and pickles in waterbath canner 
Water freezes 
Growth of bacteria is stopped, but bacteria level before freezing 
remains constant and not reduced 
Keep frozen foods in this range 
Water boils 
Most bacteria destroyed 
No growth, but survival of some bacteria 
Hottest temperature hands can stand 
Extreme DANGER ZONE. Rapid growth of bacteria and production 
 of poisons by some bacteria 
Body temperature – ideal for bacterial growth 
40 
Slow growth of some bacteria that cause spoilage 
Some growth of food poisoning bacteria may occur D
A
N
G
E
R
 Z
O
N
E
Source: Keeping Food Safe to Eat, USDA 
Epidemiology (Schneider) 
Bacterial Growth Curve 
N
u
m
b
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o
f 
C
e
lls
Time 
Decline Phase 
Stationary Phase 
Log Phase 
Lag Phase 
Epidemiology (Schneider) 
Effect of Temperature in 
Salmonella Growth 
N
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S
a
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lla
 p
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g
ra
m
Days 
2 1 4 5 3 
95oF (35o C) 
50oF (10o C) 
44oF (6.7o C) 
42oF (5.5o C) 
Incubation Periods 
2-4 hours Staphylococcus aureus Cooked ham, meat, 
eggs, sauces and gravies 
12 hours Clostridium perfringens Cooked meats, gravy 
12-36 hours Salmonella* Meat, poultry, eggs 
12-36 hours Clostridium botulinum Canned foods, smoked 
fish 
12 hours Vibrio parahemolyticus* Raw fish, shellfish 
24-48 hours Shigella* Contaminated by carrier, 
not foodborne 
* Fever 
National Data on Etiology of Foodborne Illness 
Agent 
Bacteria (40 agents) 68.7% 
 Salmonella 25.0% 
 Staph. aureus 12.7% 
 Clostridium perfringens 10.0% 
 Clostridium botulinum 9.5% 
Viral (11 agents) 9.4% 
Parasites (31 agents) 0.5% 
Fungal (16 agents) 1.8% 
Plants (36 agents) - 
Fish (28 agents) 12.3% 
Chemicals (28 agents) 7.3% 
 On April 19, 1940, the local health 
officer in the village of Lycoming, 
Oswego County, New York, reported 
the occurrence of an outbreak of acute 
gastrointestinal illness to the District 
Health Officer in Syracuse. Dr. A. M. 
Rubin, epidemiologist-in-training, was 
assigned to conduct an investigation. 
When Dr. Rubin arrived in the field, he learned from the health 
officer that all persons known to be ill had attended a church 
supper the previous evening, April 18. Family members who 
had not attended the church supper had not become 
ill. Accordingly, the investigation was focused on the 
circumstances related to the supper. 
 Source: CDC 
Investigating an Epidemic: Oswego, NY 
Epidemiology (Schneider) 
Interviews regarding the presence of symptoms, including 
the day and hour of onset, and the food consumed at the 
church supper, were completed on 75 of the 80 persons 
known to have been present. A total of 46 persons who had 
experienced gastrointestinal illness were identified. 
Q: Is this an Epidemic? 
 Endemic for the region? 
 Due to seasonal variation? 
 Due to random variation? 
 Select the correct case definition 
 and find the error in the others: 
1. All participants in the Oswego church supper held in the basement of 
the church in Lycoming, Oswego County, New York, on April 18, 1940, 
between 6:00 PM and 11:00 PM; whether they attended church or not; 
whether they participated in food preparation, transport, or distribution 
or not; whether they ate or not. 
2. Persons who developed acute gastrointestinal symptoms within 72 
hours of eating supper on April 18, 1940, and who were among 
attendees of the Lycoming, Oswego Church supper. 
3. Church members who developed acute gastrointestinal symptoms 
within 72 hours of the church supper held in Lycoming, Oswego on 
April 18, 1940. 
 Select the correct case definition 
 and find the error in the others: 
1. All participants in the Oswego church supper held in the basement of 
the church in Lycoming, Oswego County, New York, on April 18, 1940, 
between 6:00 PM and 11:00 PM; whether they attended church or not; 
whether they participated in food preparation, transport, or distribution 
or not; whether they ate or not. 
2. Persons who developed acute gastrointestinal symptoms within 72 
hours of eating supper on April 18, 1940, and who were among 
attendees of the Lycoming, Oswego Church supper. 
3. Church members who developed acute gastrointestinal symptoms 
within 72 hours of the church supper held in Lycoming, Oswego on 
April 18, 1940. 
 Select the correct case definition 
 and find the error in the others: 
1. All participants in the Oswego church supper held in the basement of 
the church in Lycoming, Oswego County, New York, on April 18, 1940, 
between 6:00 PM and 11:00 PM; whether they attended church or not; 
whether they participated in food preparation, transport, or distribution 
or not; whether they ate or not. Missing definition of sickness 
2. Persons who developed acute gastrointestinal symptoms within 72 
hours of eating supper on April 18, 1940, and who were among 
attendees of the Lycoming, Oswego Church supper. CORRECT 
3. Church members who developed acute gastrointestinal symptoms 
within 72 hours of the church supper held in Lycoming, Oswego on 
April 18, 1940. Did not specify that they went to the dinner 
Incidence of Cases of Diarrhea Among People Attending Lycoming,Oswego Church Supper, June 1940 
Epidemiology (Schneider) 
The supper was held in the basement of the village 
church. Foods were contributed by numerous 
members of the congregation. The supper began at 
6:00 PM and continued until 11:00 PM. Food was 
spread out upon a table and consumed over a period 
of several hours. 
Epidemiology (Schneider) 
Main Dishes • Baked ham 
• Spinach 
• Mashed potatoes 
• Cabbage salad 
• Fruit Salad 
Side Dishes • Jello 
• Rolls 
• Brown Bread 
Desserts • Cakes 
• Vanilla Ice Cream 
• Chocolate Ice Cream 
Beverages • Milk 
• Coffee 
• Water 
Church Supper Menu 
Epidemiology (Schneider) 
Which menu item(s) is the potential culprit? 
To find out, calculate attack rates. 
The foods that have the greatest difference in attack 
rates may be the foods that were responsible for the 
illness. 
Epidemiology (Schneider) 
Attack Rates by Items Served: Church Supper, Oswego, New York; April 1940 
Number of persons who ate 
specified item 
Number of persons who did not eat 
specified item 
Ill Well Total Attack rate (%) Ill Well Total Attack rate % 
Baked ham 29 17 46 17 12 29 
Spinach 26 17 43 20 12 32 
Mashed potato 23 14 37 23 14 37 
Cabbage salad 18 10 28 28 19 47 
Jello 16 7 23 30 22 52 
Rolls 21 16 37 25 13 38 
Brown bread 18 9 27 28 20 48 
Milk 2 2 4 44 27 71 
Coffee 19 12 31 27 17 44 
Water 13 11 24 33 18 51 
Cakes 27 13 40 19 16 35 
Ice cream (van) 43 11 54 3 18 21 
Ice cream (choc) 25 22 47 20 7 27 
Fruit salad 4 2 6 42 27 69 
Attack Rates by Items Served: Church Supper, Oswego, New York; 
April 1940 
Number of persons who ate 
specified item 
Number of persons who did not eat 
specified item 
Ill Well Total Attack rate (%) Ill Well Total Attack rate % 
Baked ham 29 17 46 63 17 12 29 59 
Spinach 26 17 43 60 20 12 32 62 
Mashed potato 23 14 37 62 23 14 37 62 
Cabbage salad 18 10 28 64 28 19 47 60 
Jello 16 7 23 70 30 22 52 58 
Rolls 21 16 37 57 25 13 38 66 
Brown bread 18 9 27 67 28 20 48 58 
Milk 2 2 4 50 44 27 71 62 
Coffee 19 12 31 61 27 17 44 61 
Water 13 11 24 54 33 18 51 65 
Cakes 27 13 40 67 19 16 35 54 
Ice cream (van) 43 11 54 80 3 18 21 14 
Ice cream (choc) 25 22 47 53 20 7 27 74 
Fruit salad 4 2 6 67 42 27 69 61 
Number of persons who ate 
specified item 
Number of persons who did not eat 
specified item 
Ill Well Total Attack rate (%) Ill Well Total Attack rate % 
Baked ham 29 17 46 63 17 12 29 59 
Spinach 26 17 43 60 20 12 32 62 
Mashed potato 23 14 37 62 23 14 37 62 
Cabbage salad 18 10 28 64 28 19 47 60 
Jello 16 7 23 70 30 22 52 58 
Rolls 21 16 37 57 25 13 38 66 
Brown bread 18 9 27 67 28 20 48 58 
Milk 2 2 4 50 44 27 71 62 
Coffee 19 12 31 61 27 17 44 61 
Water 13 11 24 54 33 18 51 65 
Cakes 27 13 40 67 19 16 35 54 
Ice cream (van) 43 11 54 80 3 18 21 14 
Ice cream (choc) 25 22 47 53 20 7 27 74 
Fruit salad 4 2 6 67 42 27 69 61 
Attack Rates by Items Served: Church Supper, Oswego, New York; 
April 1940 
Highlighted row indicates largest difference between attack rates 
Attack Rate by Consumption of Vanilla Ice 
Cream, Oswego, New York; April 1940 
Ill Well Total Attack Rate 
(%) 
Ate vanilla 
ice cream? 
Yes 43 11 54 79.6 
No 3 18 21 14.3 
Total 46 29 75 61.3 
• The relative risk is calculated as 79.6/14.3 or 5.6 
• The relative risk indicates that persons who ate 
vanilla ice cream were 5.6 times more likely to 
become ill than those who did not eat vanilla ice 
cream 
Epidemiology (Schneider) 
Conclusion 
 An attack of gastroenteritis occurred following a church supper 
at Lycoming 
 The cause of the outbreak was most likely contaminated 
vanilla ice cream 
Epidemiology (Schneider) 
Surveillance 
Ongoing systematic collection, collation, analysis 
and interpretation of data; and the dissemination of 
information to those who need to know in order 
that action may be taken. 
 World Health Organization 
Epidemiology (Schneider) 
Purposes of Public Health Surveillance 
 Estimate magnitude of the problem 
 Determine geographic distribution of illnesses 
 Portraying the natural history of disease 
 Detect epidemic / Define a problem 
 Generate hypotheses and stimulate research 
 Evaluate control measures 
 Monitor changes in infectious agents 
 Detect changes in health practice 
 Facilitate planning 
CDC 
Epidemiology (Schneider) 
Passive Surveillance 
 Physicians, laboratories, and hospitals are given forms 
to complete and submit with the expectation that they 
will report all of the cases of reportable disease that 
come to their attention 
 Advantages: Inexpensive 
 Disadvantages: Data are provided by busy health 
professionals. Thus, the data are more likely to be 
incomplete and underestimate the presence of disease 
in the population 
Epidemiology (Schneider) 
Active Surveillance 
 Involves regular periodic collection of case reports by 
telephone or personal visits to the reporting individuals to 
obtain the data 
 Advantages: More accurate because it is conducted by 
individuals specifically employed to carry out the 
responsibility 
 Disadvantages: Expensive 
Epidemiology (Schneider) 
Sentinel Surveillance 
 Monitoring of key health events, through sentinel sites, 
events, providers, vectors/animals 
 Case report indicates a failure of the health care system or 
indicates that special problems are emerging 
 Advantages: Very inexpensive 
 Disadvantages: Applicable only for a select group of 
diseases 
Epidemiology (Schneider) 
Some Surveillance Programs 
 National Notifiable Diseases Surveillance System 
 Morbidity and Mortality Weekly Report (MMWR) 
 Cancer Surveillance, Epidemiology and End Result 
(SEER) 
Epidemiology (Schneider) 
“Good surveillance does not necessarily ensure 
the making of right decisions, but it reduces the 
chances of wrong ones.” 
 Alexander D. Langmuir 
 NEJM 1963;268:182-191