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 
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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Source: CDC, unpublished data, 1978 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