Exposure of uninfected poultry farms to HPAI (H7N7) virus by professionals during outbreak control activities.

With an extensive data set on visits made to control the H7N7 avian influenza epidemic in The Netherlands in 2003 we investigate the potential role of the persons involved in the control activities as vectors for disease transmission. We hypothesized that people can spread the virus on the same day mechanically, or till 10 days if they have become infected themselves. Taken into account was the estimated time of introduction of the virus into a poultry flock back-calculated from mortality data. We identified 19 visits from a person that went on the same day from an infected (source) farm to a (target) farm that was before infection and a further 197 visits were made to (target) farms that remained uninfected. Of the 19 visits, eight were made within 3 days before an infection started on the target farm. If we assume that these eight visits were the primary reason the visited farms became infected, then we can calculate an upper estimate for the probability of transmission by a person per visit of 0.037. In addition we identified visits were a person first visited an infected source farm and up to 10 days after visited a target farm that either remained uninfected or was before infection. Most visits to infected source farms were made just after infection. Animals on these farms were likely not yet symptomatic, thus escaping diagnosis. Such events may be difficult to prevent, although awareness of this possibility is already a major step towards prevention. Most of these visits involved tracing and screening and were made by a relatively small number of trained veterinarians. This makes it possible to focus training efforts specifically on these persons and make sure they stringently use the personal protective equipment and strictly follow the hygiene protocol, to protect them and prevent them from spreading the disease.

Case-control study on the association between a cluster of childhood haematopoietic malignancies and local environmental factors in Aalsmeer, The Netherlands.

STUDY OBJECTIVE AND DESIGN: In Aalsmeer, a horticultural community near the main international airport in The Netherlands, a more than fourfold increase in the incidence of haematopoietic malignancies in young people was observed between 1980 and 1985. In a population based case-control study, the association with local environmental factors was investigated. PARTICIPANTS: For each patient younger than 40 years of age (n = 14) diagnosed between 1975 and 1989, four age and sex matched controls were selected via local general practitioners. METHODS: All parents of patients and controls completed a questionnaire on their lifestyle, living conditions, and health, for several years preceding each individual diagnosis. Odds ratios (ORs) with 95% confidence intervals (CI) were calculated, matched, and, if necessary, stratified for neighbourhood. MAIN RESULTS: Increased ORs were recorded for intensive use of petroleum products and pesticides by the patients themselves and their fathers: OR petroleum products: 8.0 (95% CI 2.2, 129.9) and 9.0 (1.0, 66.1) respectively; OR pesticides: 6.0 (0.6, 49.3) and 3.2 (1.0, 10.1) respectively. Swimming in a local pond was also significantly associated with the disease: OR = 5.3 (1.3, 17.4). In the 1970s this pond had been polluted by petroleum products and pesticides. CONCLUSIONS: The increased incidence of childhood haematopoietic malignancies in Aalsmeer may have been associated with several specific local environmental factors. Interpretation of the results, however, should take into account the fact that confidence intervals were wide because of the limited number of cases.

[Case control study of the relationship between local environmental factors and hematopoietic malignancies in young subjects in Aalsmeer]. / Patiënt-controle-onderzoek naar het verband tussen lokale milieufactoren en hematopoëtische maligniteiten bij jongeren in Aalsmeer.

In Aalsmeer, a horticultural community near the main international airport in the Netherlands, an incidence of haematopoietic malignancies in young people over four times the national mean was observed in the period 1980-1985. A population based case-control study investigated the association with local environmental factors. For each case younger than 40 years of age (n = 14), diagnosed between 1975 and 1989, four controls, matched for age and gender, were selected via local general practitioners. All parents of patients and controls completed a questionnaire on their life style, living conditions and health for several years preceding each individual diagnosis. Odds ratios (ORs) were calculated, matched and--if necessary--stratified for neighbourhood. Increased ORs were recorded for intensive use of petroleum products and pesticides, by the patients themselves and their fathers (OR petroleum products: 8.0, resp. 9.0; OR pesticides: 6.0, resp. 3.2). Most of these increases were statistically significant. Swimming in a local pond was also significantly associated with the disease (OR = 5.3); in the seventies this pond had been polluted by accidents with petroleum products and pesticides. contributed to the increase of the disease: ORs for several indirect exposure parameters were all above 2. It can be concluded that the increased incidence of childhood haematopoietic malignancies in Aalsmeer may have been associated with several specific local environmental factors. However, interpretation of the results should take into account that confidence intervals were wide, due to the necessarily limited number of cases.