1. ¹Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA
2. ²Division of Epidemiology, School of Public Health, University of California, Berkeley, CA, USA
3. ³King's College London, Academic Centre for Defence Mental Health, Institute of Psychiatry, London, UK
4. ⁴Division of Cardiovascular Medicine, Oregon Health and Science University, Portland, OR, USA
5. ⁵Department of Biostatistics, Boston University, Boston, MA, USA
6. ⁶Department of Pediatrics, Kaiser Permanente Santa Clara Medical Center, Santa Clara, CA, USA
7. ⁷Department of Pediatric Hematology/Oncology, Kaiser Permanente, Sacramento, CA, USA

Correspondence: Dr JS Chang, Department of Epidemiology and Biostatistics, University of California, 44 Page Street, Suite 503, San Francisco, CA 94143-1215, USA. E-mail: jeffrey.chang@ucsf.edu

Received 18 August 2007; Revised 5 September 2007; Accepted 7 September 2007; Published online 9 October 2007.

Abstract

To study the possible relation between parental social contact through occupation, a marker for a child's risk of infection, and childhood acute lymphoblastic leukaemia (ALL), the parents of 294 children with ALL aged 0–14.9 years and 376 matched controls were interviewed about their jobs after their child's birth up to the age of 3 years. Job titles were assigned to a level of social contact, and an index of occupational social contact months was created using the level and the job duration. Positive interactions between this index and rural residence associated with an increased risk of childhood ALL and common ALL (c-ALL) were observed (interaction P-value=0.02 for both, using tertiles of contact months; interaction P-value=0.05 and 0.02 for ALL and c-ALL, respectively, using continuous contact months); such findings were not observed when job durations were ignored. Our data suggest that duration of parental occupation may be important when examining the association between parental social contact in the workplace and childhood leukaemia.