Develop a case definition

MANUAL OF NAVAL PREVENTIVE MEDICINE

about: the person (name, rate/rank, social security number, residential

address or work/berthing as assignments, duty station, age, race, sex, and

telephone number); their illness, if any (specific symptoms and specific

times at which symptoms developed), and food history (when, where and what

was eaten, as precisely as possible). The time at which food was eaten and

symptoms started must be recorded precisely, e.g.,"0100" or "1245."

Responsible persons should interview and complete a questionnaire for each

person.

(3) Establish a diagnosis etiologically if possible, otherwise

define cases clinically or epidemiologically. Obtain clinical specimens

from patients, for laboratory analysis to isolate or identify the etiologic

agents. Ideally, specimens should be collected during the acute phase of

the illness when the patient is first seen or when the initial interview is

conducted. Convalescent specimens collected after the patient recovers may

be useful for comparison. If the patient has diarrhea, obtain a stool

specimen or rectal swab. If the person is vomiting, collect vomitus.

Blood specimens are used to detect antibodies, or isolate pathogens. Blood

and/or urine specimens may also be useful in confirming diagnosis of

chemical food poisoning. Contact the laboratory officer at the nearest

medical treatment facility or NAVENPVNTMEDU for guidance on collecting,

storing, and shipping samples for analysis. If the demand for laboratory

analyses exceeds the capability of the MTF laboratory, contact the nearest

NAVENPVNTMEDU. The units maintain a public health laboratory capability to

conduct analysis of clinical specimens from an outbreak investigation or

can assist in arranging for appropriate laboratory analysis.

(4) Collect food samples and/or containers. If food items are

leftover from a suspect meal, or if a commercial product is suspected,

collect and preserve samples for laboratory analysis. Remaining stocks of

suspect food should not be used until the investigation is complete. Use

aseptic techniques and containers to collect samples; seal and label each

container. Collect a sample of each item weighing to 1 pound or measuring

to 1 pint, if less is available collect all of it. Samples of perishable

foods should be chilled and held below 41F (4C) but should not be frozen.

Commercial foods in containers (e.g., jars or cans) should be kept in

those containers. Empty containers of suspect commercial products should

also be collected and preserved. Contact the nearest NAVENPVNTMEDU for

additional guidance on collecting, storing and shipping samples for

analysis. NAVENPVNTMEDU laboratories can analyze food samples or can

assist in arranging for appropriate laboratory analyses.

d. Develop a case definition. A case definition allows exposed persons

to be classified as either cases or non-cases. A case is usually defined

by symptoms, e.g., a person who was at risk and developed diarrhea (3 or

more watery stools within a 24-hour period), and a time frame. Use the

data collected during the initial phase of the investigation to establish

the definition. A case definition may be specific, e.g., diarrhea and

fever (temperature greater than 100.5F) or more general, (e.g., diarrhea,

nausea or vomiting with or without fever). Cases can be categorized

128