Creating a trawling questionnaire for a Legionnaires' disease outbreak
A template trawling questionnaire is available here and an EpiInfo
version here. The rest of this page considers why and
how one might conduct a trawling questionnaire.
Hypothesis generation is a critical step in an outbreak situation. By administering an
open-ended hypothesis-generating questionnaire to some of the first
case-patients the investigator(s) will attempt to learn about potential exposures to known risk
factors. This information can be viewed as a line listing and from this,
along with results from a literature review if appropriate, specific hypotheses about the cause
of the outbreak can be formulated. Often these hypotheses will become the basis of a second
structured hypothesis-testing questionnaire which itself can be used to test these hypotheses
in an analytical study. Please note the trawling nature of hypothesis
generating questionnaires will usually be much more exhaustive in their questions than those
associated with more standard surveillance operations (See version of surveillance questionnaire in EpiInfo format).
Objectives of a trawling interview (hypothesis-generating) questionnaire
trawling interview questionnaire
- to gather preliminary data to:
- generate hypotheses as to the potential source/cause of the outbreak so that control
measures can be applied to prevent further cases.
- highlight aspects of the investigation that demand collection of additional or more
The age, education level and other characteristics of the case-patients will guide the language
used in the interview to ensure that questions are approached in a culturally-sensitive and
appropriate way particularly if some areas of questioning are uncomfortable. Having memory
prompts available, such as calendars, may help case-patients remember details.
Use a combination of closed-ended (e.g. yes/no) and open-ended questions in a
trawling questionnaire. Closed-ended questions are easier to standardise, code and analyse, but
they may not provide complete or exhaustive detail. Open-ended questions are less constrained,
which allows interviewees to express themselves freely, but they are more difficult to code and
If feasible, it is preferable for one person, or an organised and trained group of people, to
conduct all of the interviews as this makes it easier to identify any commonalities or peculiar
findings. The interviewer should have sufficient background knowledge of Legionnaires' disease,
as well as have good interviewing and people skills. Additionally, the interviewer must be
professional but friendly, and should show concern for the well-being of the case-patient.
Additional interview guidance is available here.
Explain the purpose of the interview, being careful not to make comments that could
bias responses, and tell the case how long the interview will take. A trawling questionnaire is,
by nature, often exhaustive and may take a relatively long time. If the length of time is too
demanding for the patient or the interview is impossible for other reasons suitable proxies for
the information can be indentified (family/friends, clinicians/nurses etc)
alternatives should be clearly stated to enable future analysis/interpretation.
Questioning should be systematic but flexible enough to allow the case-patient to provide
comments that may give additional insights into the cause of the outbreak. Once the interview
is completed, provide contact information, thank the interviewee for participating, and
acknowledge his or her contribution to the investigation.
Sources for template trawling questionnaire
b) Vertaalde versie van Legionellose bijlage 1 December 2007.doc. Holland.
c) Surrey and Sussex Health Protection Unit, United Kingdom