4. 1 verification diagnosis
After arriving at the scene, the investigation team should verify the incidence, interview patients and collect patient specimens and food samples.
(1) Validation incidence. Understand the main clinical features, diagnosis and treatment of patients through attending physicians, consult the patient's medical records and clinical laboratory test reports in attending medical institutions, and extract and copy relevant information.
(2) Conduct case interviews. According to the accident situation, make an interview outline, determine the number of interviews, and conduct case interviews. Respondents tend to be in special situations such as the first situation and the last situation; The interview content mainly includes demographic data, onset and treatment, diet history before onset, etc. For the interview outline, see the Outline of Food Safety Accident Case Interview (Attached Table 3- 1).
(3) collecting samples. Investigators should immediately collect biological specimens of cases, environmental samples of food and processing places and biological specimens of food practitioners after arriving at the scene. For the methods of sample collection, preservation and transportation, please refer to the Requirements for Sample Collection, Preservation and Transportation of Food Safety Accidents (Appendix 4) and the Requirements for Clinical Manifestations, Latency and Biological Specimen Collection of Common Pathogenic Factors of Food Safety Accidents (Appendix 5). If no relevant samples are collected, records shall be made and the relevant reasons shall be explained in the investigation report.
4.2 Develop a case definition
The definition of a case should be concise and operable, and can be adjusted with the progress of investigation. A case definition may include the following:
(1) time: limit the accident time range;
(2) Area: Limit the accident area;
(3) Crowd: limit the scope of accident crowd;
(4) Symptoms and signs: Symptoms and signs that are common in most cases or unique to accident-related cases are usually adopted. Symptoms such as dizziness, headache, nausea, vomiting, abdominal pain, diarrhea, acute diarrhea, convulsions, etc. Signs such as fever, cyanosis, miosis, pathological reflex, etc.
(5) Positive results of clinical auxiliary examination: including clinical laboratory examination, imaging examination and functional examination, such as eosinophilia and methemoglobin.
(6) Specific drugs are effective: drugs only have obvious effects on specific pathogenic factors. For example, methylene blue therapy can effectively prompt nitrite poisoning, and anti-botulinum toxin therapy can effectively prompt botulinum toxin poisoning.
(7) The test result of pathogenic factors is positive: the biological specimen of the case or the sample of leftovers eaten by the case is positive.
Case definition can be divided into suspected cases, possible cases and confirmed cases. The definition of suspected cases usually refers to the nonspecific symptoms and signs of most cases; The definition of possible cases usually means that there are specific symptoms and signs, or the clinical auxiliary examination results of suspected cases are positive, or the suspected cases have effective treatment with specific drugs; The definition of confirmed cases usually refers to the definition of suspected cases or possible cases, and has a positive result of pathogenic factor detection.
At the beginning of the investigation, we can use the highly sensitive definition of suspected cases to search for cases and make descriptive epidemiological analysis of all cases (including suspected, possible and confirmed cases). In the analytical epidemiological study, the definitions of possible cases and confirmed cases with high specificity should be adopted to analyze the correlation between the incidence and suspicious exposure factors.
4.3 Conduct case search
The investigation team shall, according to the specific circumstances, choose appropriate methods to conduct case search, and may refer to the following methods to conduct case search:
(1) For accidents with definite suspicious meal time, such as food poisoning caused by dinner, you can search all cases by collecting the list of people attending dinner;
(2) For accidents in factories, schools, nurseries or other collective units, the person in charge of the collective unit or the school doctor (factory doctor) may be required to collect people who may be sick by collecting absenteeism records, morning check-up records and school doctor (factory doctor) records;
(3) When the accident involves a small area or the incident is relatively concentrated, or there are deaths or serious cases, the method of household search can be adopted;
(4) If the accident involves a large range or a large number of cases, the administrative department of health should be advised to organize medical institutions to consult outpatient logs, access registration, inspection report registration, etc. , and search and report cases that meet the definition of cases;
(5) The accident involves food in circulation in the market, and the food is widely sold or the flow direction is uncertain, or the accident has a great impact. We should collect and analyze relevant case reports through the disease monitoring and reporting system, or suggest that the health administrative department release early warning information to the society, set up a consultation hotline, and search for cases by urging similar patients to see a doctor.
When searching for cases, you can use the list to record the onset time and clinical manifestations of cases. For the list, please refer to Clinical Information List of Food Safety Accident Investigation Cases (Table 3-2).
4.4 Conduct case investigation
4.4. 1 survey method
According to the education level and cooperation degree of the case, combined with the requirements of case search method, face-to-face interview survey, telephone survey or self-filled questionnaire survey can be selected. Case investigation can be combined with case search and carried out at the same time. Case investigation should use checklist or case questionnaire, and adopt the same investigation method. The scope of case investigation should be determined according to the needs of accident investigation and available investigation resources, so as to avoid delaying the follow-up investigation due to the completion of all case investigations.
4.4.2 Investigation contents
The information to be collected in case investigation mainly includes:
(1) Demographic information: including name, gender, age, nationality, occupation, address, contact information, etc.
(2) Incidence and diagnosis and treatment: symptoms, signs, occurrence and duration of onset, secondary symptoms, signs and duration, diagnosis and treatment and disease prognosis, laboratory examination items and results, etc. ;
(3) Diet history: the number of meals, the type and quantity of food eaten at each meal, the time and place of eating, all other foods except normal meals, such as snacks, drinks, fruits, drinking water, special food handling and cooking methods. ;
(4) Information on other personal high-risk factors: history of going out, contact with similar cases, contact with animals, history of basic diseases, allergy, etc.
4.4.3 Design case questionnaire
For the design of the list, please refer to Schedule 3-2 and Food Exposure Information List of Food Safety Accident Investigation Cases (Schedule 3-3). The case questionnaire can be designed with reference to the following characteristics of different accidents:
(1) The case had only one meal with the same exposure before the onset, and the questionnaire can be designed with reference to the Questionnaire on Food Safety Accidents Caused by Dinner (Table 3-4).
(2) Before the onset of the case, there were many * * * meals exposed. Please refer to the Questionnaire on Food Safety Accidents in Schools and Other Collective Units (Table 3-5) to design the questionnaire.
(3) There is no obvious epidemiological relationship between cases. For example, diarrhea outbreaks among residents in several communities can be designed with reference to community food safety accident case questionnaires (Table 3-6).
4.5 Descriptive epidemiological analysis
After the case investigation, a database should be established according to the list or case questionnaire, and the collected information should be entered in time. After checking the input data, descriptive epidemiological analysis should be carried out according to the following contents.
4.5. 1 clinical features
Clinical characteristics analysis should count the number and proportion of patients with various symptoms and signs, and sort them according to the proportion. For example, see table 1. According to the clinical distribution characteristics, the possible range of pathogenic factors can be preliminarily analyzed with reference to Appendix 5.
Table 1 Analysis of clinical characteristics of a food safety accident (n= 125) Proportion (%) Diarrhea 103 82 Abdominal pain 65 52 Fever 5 1 4 1 headache 48 38 Dizziness 29 23 Vomiting 25 20 Nausea 2/.
The time distribution can be described by epidemic curve, which can directly show the stage of accident development, describe the spread mode of disease, infer the possible exposure time and reflect the effect of control measures. For the application of epidemic curve, please refer to the application of epidemic curve in descriptive epidemiological analysis (Appendix 6). Histogram is a common form of popular curve, and the method of drawing histogram is as follows:
(1) With the onset time as the horizontal axis (X axis) and the number of patients as the vertical axis (Y axis), the histogram was drawn;
(2) The time on the horizontal axis can be days, hours or minutes, and the interval should be equidistant, generally less than1/4 of the average incubation period of the disease; If the incubation period is unknown, you can try to draw at various time intervals and choose the most suitable epidemic curve;
(3) The average incubation period of 1-2 disease should be maintained before and after the first case. If the onset has not stopped at the time of investigation, there is no time interval after the last case;
(4) Mark some special events or environmental factors on the pop music line, such as starting an investigation and taking control measures. See figure 1 for an example.
Figure 1 epidemic curve of a food safety accident (omitted)
area distribution
Describe the regional distribution of accidents by drawing punctuation or regional maps.
Punctuation chart (1) can clearly show the clustering of cases and the influence of related factors on disease distribution, which is suitable for accidents with fewer cases. Mark the location of the case (or the family, class or school where the case is located) with symbols such as dots or serial numbers on hand-drawn sketches, plane maps or electronic maps, and analyze the relationship between the clustering of case distribution and environmental factors. As shown in Figure 2, the family members of rodenticide poisoning cases mainly gathered around a canteen, suggesting that the incident may be related to the food sold in a canteen.
Figure 2 Distribution of 6 families poisoned by anticoagulant rodenticide in a village (omitted)
(2) The regional map is suitable for large-scale and cross-regional accidents. Using the prevalence rates of different areas (provinces, cities, counties/districts, streets/towns, neighborhood committees/villages), and drawing with map software such as EpiInfo or MapInfo, the differences of diet, drinking water and other factors between high prevalence areas and low prevalence areas or case-free areas are analyzed, for example, as shown in Figure 3.
Figure 3 20 1 1 year EHEC o104: Regional distribution of cases of hemolytic uremic syndrome (HUS) during H4 outbreak (omitted).
Population distribution
According to the characteristics of population such as gender, age (grade is commonly used in schools or kindergartens instead of age) and occupation, this paper analyzes whether there is statistical difference in the incidence rate of each population, so as to infer the high-risk population, compare the similarities and differences of dietary exposure among the population with statistical differences, and find the clues of etiology. Examples are shown in Table 2.
Table 2 Age distribution of a food safety accident case The number of cases (years old) in this age group (%) 0-3374455-15364210-13220-18912030.
4.5.5 Analysis of Descriptive Epidemiological Results
According to the interviewed cases, clinical characteristics and epidemiological distribution, descriptive epidemiological analysis should be put forward to make a preliminary judgment on the pathogenic factors, suspicious meals and suspicious foods that caused the accident, so as to guide clinical treatment, food hygiene investigation and laboratory inspection, and put forward suggestions on prevention and control measures.
4.6 Analytical epidemiological study
Analytical epidemiological research is used to analyze the correlation between suspicious food or diet and the incidence, and case-control study and cohort study are often used.
After the descriptive epidemiological analysis is completed, analytical epidemiological research should be continued if the following situations exist.
(1) Descriptive epidemiological analysis was not supported by food hygiene investigation and laboratory test results;
(2) Descriptive epidemiological analysis can't judge suspicious meals and suspicious foods;
(three) the accident has not been effectively controlled or the risk of recurrence;
(4) The investigation team considers it necessary to continue the investigation.
4.6. 1 Case-control study
When it is difficult to investigate all accident cases or the people exposed to accidents are uncertain, it is suitable to carry out case-control research.
(1) Respondents. Case group and control group were selected as the research objects. The case group should choose confirmed cases or possible cases as far as possible. The number of cases is small (
(2) Investigation methods. According to the results of preliminary judgment, a questionnaire about suspicious diet or suspicious food was designed (refer to attached tables 3-4, 3-5 and 3-6), and the consistency of the case group and the control group was investigated to collect information about eating suspicious food or all foods in suspicious diet and eating various foods.
(3) Calculate the OR value. AccORding to the number of meals or food types, the ratio (OR) and 95% confidence interval (CI) of eating and not eating in the case group and the ratio of eating and not eating in the control group were calculated. For example, when OR> 1 and 95%CI does not include 1, it can be considered that the correlation between the meal or food and the disease is statistically significant; If there are two or more suspicious meals or foods, hierarchical analysis and multivariate analysis can be used to control the influence of mixed factors. For the confirmed suspicious food, please refer to the data analysis method of analytical epidemiological research for further analysis of dose-response relationship (Appendix 7).
4.6.2 Queue research
When the number of people exposed to accidents has been determined and the number is small, it is suitable to carry out cohort study.
(1) Respondents. Take all the people you come into contact with as the research object, such as all the people who attend the dinner, all the customers who eat in the restaurant, the students in the school, the workers in the factory, etc.
(2) Investigation methods. According to the results of preliminary judgment, a questionnaire about suspicious diet or suspicious food was designed (refer to attached tables 3-4, 3-5 and 3-6), and all subjects were investigated individually, and information such as the onset of illness, the consumption of suspicious food or all foods in suspicious diet and the consumption of various foods were collected.
(3) Calculate RR value. According to the dietary or food intake, the patients were divided into exposed group and unexposed group, and the ratio (RR) and 95%CI of the incidence of each dietary or food exposure group to that of the unexposed group were calculated. For example, when RR> 1 and 95%CI does not include 1, it can be considered that the correlation between the meal or food and the disease is statistically significant. If there are two or more suspicious meals or foods, hierarchical analysis and multivariate analysis can be used to control the influence of mixed factors. For the identified suspicious food, please refer to Appendix 7 for further dose-response analysis.