June 23, 2011

Perth County - The Perth District Health Unit has released its report on the Hodgkin Lymphoma Cluster Investigation that began in October 2010. The investigation was begun to look into what appeared to be increased rates of Hodgkin Lymphoma in Perth County teenagers.

“The purpose of the investigation was to better understand the situation, to seek potential known or unknown risk factors, share the information with the community, and to make recommendations, if possible,” explains Dr. Miriam Klassen, Acting Medical Officer of Health.

As part of its investigation, the Health Unit conducted a case series study, which involved interviewing 11 cases affected by Hodgkin Lymphoma (HL). Seven of these cases met the complete study criteria and the results of their interviews are analyzed in the report.

“We feel very thankful to the families who took part in our investigation,” says Dr. Klassen. “Their participation meant we were able to collect important information to better understand what is happening in our community.”

Key Findings of the Investigation
Hodgkin Lymphoma Rates in Perth County

• The rates of HL in Perth County youth aged 15 to 19 years old were higher than the Ontario rates from 1986 to 2007. They were the highest rates in Ontario over this time period.
• The rates of HL in youth aged 15 to 19 years old in surrounding health units were not elevated.
• There are approximately two cases of HL in Perth County youth every three years, making it an uncommon illness.
• The small number of cases makes it difficult to form valid conclusions.

Causation

• As with other cancer cluster investigations, no cause is suggested by our study.
• Study limitations that make it difficult to find a single cause include: the latency period of HL (three to seven years), the multifactorial nature of cancer, and the small numbers who participated in our study.

Social Clustering

• The cluster appears to be centred around the City of Stratford.
• All seven of the cases lived within a 15km radius of Stratford five to 10 years before diagnosis. This is not unexpected given that Stratford is the most populous area of Perth County.
• This geographic grouping is consistent with other HL cluster investigations presented in medical studies.
• Three cases reported knowing another person with HL and the mothers of three cases went to high school together.
• Three cases reported a family history of lymphoma. Genetic predisposition is a known risk factor for HL.
• It has been suggested that a social factor, such as an unknown infectious agent, may be involved in such clusters.

Other findings

• Some factors that were common to all cases: exposure to pesticides, time spent on farms, and chickenpox. However, these exposures have not been associated with HL and are also common to many Ontario youth and do not stand out as probable contributing factors to this cluster.
• All seven cases attended high school in Stratford: St. Michael (4), Northwestern (2) and Stratford Central (1). There is nothing to indicate that these high schools are different from other high schools in Ontario. The increase in HL in Perth County began before the new St. Michael school was constructed.
• None reported having had mononucleosis, which has been associated with HL.

“This type of social clustering of Hodgkin Lymphoma has been previously described in medical literature,” says Dr. Klassen. “Researchers have raised the theory that an unknown infectious agent may be at work when this type of grouping occurs. We believe that may be what is going on in Perth County as well.”

Next Steps
Following this investigation, the Health Unit will continue to work with Cancer Care Ontario to monitor the rates of HL in Perth County youth aged 15 to 19 years old. “While the elevated rates in our community are worth keeping an eye on, it’s important for residents to understand that HL continues to be an uncommon illness and the number of Perth County youth affected is small,” says Dr. Klassen.

The Perth District Health Unit is encouraging residents to join the Ontario Health Study at www.ontariohealthstudy.ca. It is a long-term research study designed to create a large database of people to better understand complex chronic diseases, such as cancer, and develop strategies for their prevention and treatment.

A copy of the Cancer Cluster Investigation report can be found at www.pdhu.on.ca and accessed through a link on the home page. For more information, call Health Line at 519-271-7600 ext 267 or toll-free at 1-877-271-7348 ext 267.

Attached: Hodgkin Lymphoma Cancer Cluster Investigation Report (PDF)