Investigating the relationship between drinking water and gastroenteritis in Edmonton: 1993 - 1998

2: Data Sources

To assess the relationship between water quality and gastroenteritis, a comprehensive database was created from data that were provided by various agencies. Extensive retrospective water quality and environmental data were collected to assess their impact on community health. Data stemming from hospitalisation use and physician-billing claims were used to create appropriate health outcome groups. A description of these data are provided in the subsequent sections.

2.1 Water Quality Parameters

Water quality data from January 1, 1993 to June 30, 1999 were provided by EPCOR Water Services, Inc. A complete list of the types of data provided are listed in Table 1. With the exception of the particle count data, dates of availability for all the measured indicators are identical for both plants. However, data that were available for analysis differed for some parameters, depending on when automated data retrieval systems were implemented. Finished water turbidity was provided in the form of 5-minute readings for all on-line filters (nine in Rossdale, twelve in E.L. Smith). To facilitate analysis using these extensive data (288 readings per filter per day), these data were summarised into daily mean, median, and maximum values. Subsequent statistical tests were used to determine the optimal parameterisation for these data.

Compared to the Vancouver study, additional variables available for analysis in this investigation included finished water particle count data. The use of particle counts is a new approach to measuring water quality. Only recently implemented, particle counts are perceived to be a more accurate proxy measure of finished water quality than turbidity. Many of the raw water parameters listed in Table 1 were also unique to this investigation, and were not examined in the Vancouver study.

Table 1: Indicators of water quality received from EPCOR Water Services, Inc.

Water Quality Parameters	Provision Dates
Finished water
* Turbidity	January 1 1993 to June 30 1999
* Particle Counts Rossdale plant E.L. Smith plant	January 1, 1998 to June 30, 1999 March 13, 1998 to June 30, 1999
Raw water
* Turbidity	January 1, 1993 to June 30, 1999
* Temperature	January 1, 1993 to June 30, 1999
* pH	January 1, 1993 to June 30, 1999
* Colour	January 1, 1993 to June 30, 1999
* Faecal coliform counts	January 1, 1994 to June 30, 1999
* Total coliform counts	January 1, 1994 to June 30, 1999

2.2 Environmental Parameters

Environmental parameters from January 1, 1993 to December 31, 1998 were provided by Environment Canada. Daily maximum and minimum temperatures in degrees Celsius, and daily precipitation measured in millimetres were used.

2.3 Socio-Economic Data

Average household income in 1995 was derived from the 1996 Census Data (Statistics Canada).

2.4 Health Outcome Data

Emergency visit data and hospitalisation admission data have been used previously to assess endemic gastroenteritis (Morris et al, 1998; Schawrtz et al, 1997). Many similarities exist between the health outcome data utilised in the Vancouver study and the current study. In the Vancouver study, a total of three different sources were used: hospitalisation admission data from the Canadian Institute for Health Information (CIHI); physician visit data from the Medical Services Plan in B.C.; and emergency room visit data from the British Columbia Childrens' Hospital. A comparison was then made among these datasets to determine consistency of results.

In the present study, two primary data sources were used: hospital admission data from CIHI; and physician-billing data from the Alberta Health Care Insurance Payment Plan. However, in contrast to the Vancouver study, it was possible to further differentiate the latter data source into three distinct categories: namely, billing that resulted from emergency room visits, physician-office visits, and long-long-term care facilities. Recognising that the various data-capture-sources would be more representative of certain populations, interpretations of the results were based on the findings from each of the four different data sources. The selection criteria for gastrointestinal cases and respiratory controls were based on the literature (Morris et al, 1998; Schwartz et al, 1987) and on the advice of general practitioners and a gastroenterologist.

2.4 a) Canadian Institute for Health Information

The Canadian Institute for Health Information receives data from approximately 85% of hospitals across Canada. Each record within this comprehensive database contains the specifics of each case admission, including the patient's date-of-birth, gender, postal code of residence, scrambled personal identifier, admission date, reason for admission, surgery type, diagnosis fields, and institute type. Only valid and complete records from January 1, 1993 to December 31, 1998 were further considered for the case and control selection process. These criteria selected patients that had a valid date-of-birth, admission date, and gender information. A postal code was also required to verify residence within Edmonton. Elective surgeries and elective admissions to acute care facilities were excluded from further investigation.

Gastrointestinal cases and respiratory controls were selected using a similar approach to that described in the Vancouver study. The 9^th revision of the International Classification of Diseases (ICD-9), published by the World Health Organisation, is designed for the classification of morbidity and mortality information for statistical purposes, and for the indexing of hospital records by disease and operations, for data storage and retrieval. Appropriate 3-digit and 4-digit ICD -9 codes were selected to designate admitted patients as gastroenteritis cases or respiratory controls.

Criteria for selecting gastroenteritis cases are outlined in Table 2. A gastroenteritis case was defined as any individual with a primary diagnosis³ of one of the ICD-9 codes marked in column A, or with a primary diagnosis of one of the ICD-9 codes marked in column B and a secondary diagnosis of one of the ICD-9 codes marked in column A.

Table 2: Criteria for selecting hospital admission gastroenteritis cases in the CIHI data source

		Case Definition 1	Case Definition 2
ICD-9	Description	Column A: 1°diagnosis	Column B: 1°diagnosis	with	Column A: 2°diagnosis
001	Cholera	X			X
002	Typhoid and paratyphoid fevers	X			X
003	Other salmonella infections	X			X
004	Shigellosis	X			X
005	Other food poisoning (bacterial)	X			X
006	Amoebiasis	X			X
007	Other protozoal intestinal diseases	X			X
008	Intestinal infections due to other organisms	X			X
009	Ill-defined intestinal infections	X			X
558*	Other noninfectious gastroenteritis and colitis	X			X
5350	Acute gastritis	X			X
5354	Other gastritis	X			X
5355	Unspecified gastritis and gastroduodenitis	X			X
5356	Duodenitis	X			X
5589	Other and unspecified noninfectious gastroenteritis and colitis	X			X
7870	Nausea and vomiting	X			X
276	Disorders of fluid, electrolyte, and acid -base balance		X
787	Symptoms involving digestive system		X
5781	Melaena		X
6910	Diaper or napkin rash		X
7806	Pyrexia of unknown origin		X
7830	Anorexia		X
7832	Abnormal loss of weight		X
7890	Abdominal pain		X

* Although labelled as "noninfectious", may in fact be an undiagnosed episode of infectious gastroenteritis.

Criteria for selecting respiratory controls are outlined in Table 3. A respiratory control was defined as any individual with a primary diagnosis³ of one of the ICD-9 codes marked in column C and without an additional diagnosis of any of the ICD-9 codes marked in column D.

Table 3: Criteria for selecting hospital admission respiratory controls in the CIHI data source

ICD-9	Description	Column C: 1°diagnosis	without	Column D: 1°or 2°or 3°diagnosis
460	Acute nasopharyngitis	X
461	Acute sinusitis	X
462	Acute pharyngitis	X
463	Acute tonsillitis	X
464	Acute laryngitis and tracheitis	X
465	Acute upper respiratory infections of multiple or unspecified sites	X
466	Acute bronchitis and bronchiolitis	X
480	Viral pneumonia	X
481	Pneumococcal pneumonia	X
482	Other bacterial pneumonia	X
483	Pneumonia due to other specified organism	X
484	Pneumonia in infectious disease classified elsewhere	X
485	Bronchopneumonia, organism unspecified	X
486	Pneumonia, organism unspecified	X
487	Influenza	X
490	Bronchitis, not specified as acute or chronic	X
491	Chronic bronchitis	X
492	Emphysema	X
493	Asthma	X
494	Bronchiectasis	X
496	Chronic airway obstruction, not elsewhere classified	X
001	Cholera			X
002	Typhoid and paratyphoid fevers			X
003	Other salmonella infections			X
004	Shigellosis			X
005	Other food poisoning (bacterial)			X
006	Amoebiasis			X
007	Other protozoal intestinal diseases			X
008	Intestinal infections due to other organisms			X
009	Ill-defined intestinal infections			X
041	Bacterial infection in conditions classified elsewhere			X
027	Other zoonotic bacterial diseases			X
070	Viral hepatitis			X
276	Disorders of fluid, electrolyte, and acid -base balance			X
520-579	Diseases of the digestive system			X
787	Symptoms involving digestive system			X
789	Other symptoms involving abdomen and pelvis			X

To prevent over-estimating the rate of illness and thus distorting the true relationship between gastroenteritis and water quality for both cases and controls, admissions with a similar diagnosis which occurred within 60 days of an initial visit were considered part of the same disease episode, and thus were not included in the analysis.

2.4 b) Alberta Health Care Insurance Payment Plan

The Alberta Health Care Insurance Payment Plan (AHCIPP) maintains a comprehensive database on all billing claims that originate from a variety of health care provider types. As with the CIHI database, each record within the AHCIPP database contains patient -specific information, including the age at time of treatment, gender, postal code of residence, scrambled personal identifier, diagnosis fields, and coded aggregate function centre type. This last field was used to differentiate between claims originating from various sources. Billing resulting from emergency room visits (EMRG), physician-office visits (PHYS), and long-term care centres ⁴ (LTC) were analysed separately.

Within each of these three data sources, records from January 1, 1993 to December 31, 1998 with a valid age, gender, and postal code within Edmonton were selected. Since only 3-digit ICD-9 codes were available in the AHCIPP database, the criteria used to select cases and controls varied slightly from the CIHI database. For these data, a gastroenteritis case was defined as an individual who was diagnosed with an intestinal infectious disease (ICD-9 codes: 001 -009, refer to Tables 2 and 3) or other "noninfectious" gastroenteritis and colitis (558). A respiratory control was defined as an individual who was given a primary diagnosis of an acute respiratory infection (460-466), pneumonia (480-483, 485-486), or asthma (493), who did not also suffer from an intestinal infectious disease (001 to 009), disease of the digestive system (520 to 579), nor any of the other gastrointestinal-related illness described in Table 3 (027, 041, 070, 276, 487, 787, 789). All repeat visits within a 60-day interval were excluded.

2.5 Assigning a Primary Water Source

As in the Vancouver study, water received at home was chosen as the primary exposure variable of interest. Therefore, to identify potential associations between water quality and gastroenteritis, the same method of assigning cases and controls to their primary water source was used. The 6-digit postal codes provided in the health outcome data were linked to a digitised postal code file (Enhanced Postal Code File, Desktop Mapping Technologies, Inc.). This procedure designates a centroid point, along with geographical co-ordinates, for each postal code region. Applying GIS overlay techniques on the digitally-mapped water service areas shown in Figure 2, Edmonton residents were linked to a primary water source based on their location of residence.