Pesticides Research Nr. 110 2007 – Health effects of predatory beneficial mites and wasps in greenhouses

Health effects of predatory beneficial mites and wasps in greenhouses

3 The epidemiological study

3.1 Aims and general study design
3.2 The greenhouses
3.3 The persons
3.4 Unexposed persons without contact to greenhouses

3.1 Aims and general study design

The study was a three-year follow up study. A group of greenhouse workers were studied including annual examinations.

Figure 3.1 The general design of the follow-up study as a time line with the annual examination from 0 to 36 mths. (run 0 to run 3, respectively). The top row shows the flow of persons in the study while the lower shows the investigations made within and between the annual examinations.

3.2 The greenhouses

The greenhouse firms were selected from the responders in a survey made in 1996 on the 205 firms culturing ornamental flowers in Funen’s county in order to get a group of greenhouses using microbiological pesticides and a group not using these products. The use of beneficial arthropods had no influence on the selection process.

The greenhouses all produced ornamental flowers covering more than a hundred different cultures. The most frequently produced culture was Christmas tree Stars which were cultured in the fall and sold up to Christmas. Other produced products of high frequency were Marguerites, Chrysanthemums, and roses (Larsen & Bælum, 2002).

3.3 The persons

A detailed description of the persons included is given in the former report of the study (Larsen & Bælum, 2002).

The persons were recruited at the 31 greenhouses which in the beginning of the study employed 773 persons of whom 456 (59 %) were willing to participate. The cause of non response was either leave from the work place the actual day or unwillingness of having taken a blood sample.

In run 1 (1998) the persons were reexamined and those employees who were present in the greenhouse and not previously included were offered participation. These were persons hired in the previous year and those who otherwise were not available at the first examinations. This resulted in an additional inclusion of 123 persons while 316 persons from run 0 were examined adding up to 436 persons.

In run 2 and run 3 no additional persons were included but all the persons who had participated in any of the previous runs were invited.

Persons who did not show up or did not want to participate were mailed a questionnaire about the reason for leaving the study.

In all, 579 persons participated in the study. Of these 262 were followed for three years, 237 participated in all the runs while 97 were followed for two years, and 74 persons were examined in two consecutive years. 146 persons were examined only once in run 0 or run 1.

The study was thereby based on 1592 single observations and 1056 person years for follow up.

		Run0	Run1	Run2	Run3
	Males	148	148	123	116
		(32 %)	(34 %)	(35 %)	(34 %)
	Females	308	291	227	224
		(68 %)	(66 %)	(65 %)	(66 %)
	Total	456	439	350	340
Age (years)	Males	34.8	34.7	35.8	36.3
		(17 - 60)	(17 - 67)	(19 - 67)	(20 - 67)
	Females	35.7	35.9	36.8	36.9
		(16 - 59)	(19 - 61)	(19 - 59)	(19 - 59)
Seniority	Males	14.9	14.5	16.0	16.8
in trade		(0 - 45)	(0 - 53)	(0 - 53)	(0 - 53)
	Females	8.5	8.7	9.4	9.5
		(0 - 38)	(0 - 38)	(0 - 38)	(0 - 38)
Seniority	Males	8.4	8.0	8.8	9.3
at the actual		(0-39)	(0-39)	(0-39)	(0-39)
workplace	Females	5.7	5.5	6.3	6.5
		(0-33)	(0-33)	(0-32)	(0-33)
Positive	Males	34	38	29	28
pricktest		(23 %)	(26 %)	(24 %)	(24 %)
	Females	49	50	43	42
		(16 %)	(17 %)	(19 %)	(19 %)
Atopy	Males	47	42	32	32
in the family		(32 %)	(28 %)	(26 %)	(28 %)
	Females	97	96	74	73
		(31 %)	(33 %)	(33 %)	(33 %)

Table 3-1. Key variables for the persons in the study. Age and seniority were at the inclusion into the study.

3.4 Unexposed persons without contact to greenhouses

As the measures of sensitization and health effects may not be specific for the exposure to the beneficial species and there may be difficulties in evaluating the individual exposure status, a group of 149 persons not related to the greenhouse trade, were included.

The samples were taken from subjects participating in a large population study, Risk Factors for the development of Asthma in Adults (Hansen et al., 2005), based on the protocol of the European multi center study ECRHS (European Community Respiratory Health Study{Kogevinas, 1999 2622 /id}).

The persons were selected among participants in the clinical examinations in Funen’s County carried out between September 2003 and February 2004. The persons were responders to a questionnaire sent to a random sample of 10.000 persons in five Danish counties. Among the 73 % responders, persons with symptoms of asthma and a healthy control group were invited to an examination including a detailed interview, standard skin prick test, lung function, bronchial provocation test, and blood samples. A protocol closely related to that used in the BIOGART study (Larsen & Bælum, 2002), although the instruments used for measuring lung function and bronchial responsiveness were different.

For each person 2 aliquots of plasma were sampled and kept frozen at -80°C until analysis.

Of the persons 71 were males and 78 females, the mean age being 34 years (ranging between 20 and 44 years). 55 persons (38 %) had self reported asthma while 68 (46 %) reported nasal allergies.

The persons were employed in different trades. In about 10 persons the information indicated employment in relation to agriculture or gardening. These persons will be excluded from the analyses.