Environmental Engineering Reference
In-Depth Information
Description
Upon confirmation that an outbreak has occurred, the investigat-
ing team should be activated and initial steps undertaken. It is not a simple matter
to quickly determine the cause of illness due to water, food, or other vehicle, but
a preliminary study of the symptoms, incubation periods, food and water con-
sumed, housing, bathing area, and sanitary conditions may provide early clues
and form a basis for formulating a quick response control action.
What is to be considered an outbreak case? The answer will require a pre-
liminary set of parameters with which to define the case (e.g., limits of time
regarding onset of the illness, symptoms of the illness, geographical boundaries
of the affected area, and microbiological description of the disease etiology). The
more rigid the definitions of parameters, the more likely it is that fewer cases
will qualify for inclusion in the outbreak. However, parameter definitions should
be flexible in relation to the availability of new information over time.
Following agreement on definition of a case, quantitative accounting of the
number of cases involved is in order. Reliability of physician diagnoses and
the collection of completed questionnaires of the type presented in Figure 1.5
are important. The information gathered from questionnaires contributes to the
medical survey. If it appears that the number of completed questionnaires is
insufficient, similar kinds of information can be collected and tabulated in the field
when assistance is available. The tabulation horizontal headings would include
the following seven categories:
1. Names of persons served food and/or water;
2. Age(s);
3. Ill — yes or no;
4. Day and time ill;
5. Incubation period in hours (time between consumption of ingestibles and
first signs of illness);
6. Foods and water served at suspected meals — previous 12 to 72 hours (foods
eaten are checked)
7. Symptoms — nausea, vomiting, diarrhea, blood in stool, fever, thirst, con-
stipation, stomach ache, sweating, sore throat, headache, dizziness, cough,
chills, pain in chest, weakness, cramps, other
Other analyses may include a summary of persons showing a particular symp-
tom such as vomiting, diarrhea, and nausea, as shown in Figure 1.5, or those using
a specific facility for calculation of incidence rates. For complete investigation
details, consult references as appropriate.
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A common method of determining the probable offending water is a
tabulation as shown in Figure 1.6, which is made from the illness questionnaire
provided in Figure 1.5 or similar version. Comparison of the attack rates for each
water will usually implicate or absolve a particular water. The water implicated
is that showing the highest percentage difference between those who ate the
specified water and became ill and those who did not eat the specified water and
