In October 2010, the Health Unit began a Cancer Cluster Investigation after learning that the rates of Hodgkin Lymphoma in Perth County teenagers appeared to be higher than the provincial average from 1986 to 2007.

Purpose of the Investigation

The purpose of the investigation was to:

  • better understand the situation
  • seek potential known or unknown risk factors
  • share the information with the community, and
  • make recommendations, if possible

The cause of a cancer cluster is often difficult to prove because:

  • Not all cancers are related even if they appear to be;
  • Cancers have a long latency period (cancer takes a long time to develop, so it is difficult to trace back to possible causes);
  • Random variation leads to ‘clusters’ occurring naturally;
  • Many cancers are multi-factorial, which means there are likely several contributing factors.

Key Findings of the Investigation

Hodgkin Lymphoma Rates in Perth County

  • The rates 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 in youth aged 15 to 19 years old in surrounding health units were not elevated.
  • There are approximately two cases of Hodgkin Lymphoma in Perth County youth every three years, making it an uncommon illness.
  • The small number of cases makes it difficult to form valid conclusions.


  • 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 Hodgkin Lymphoma (three to seven years), the multi-factorial 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 15 kilometers 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 Hodgkin Lymphoma cluster investigations presented in medical studies
  • Three cases reported knowing another person with Hodgkin Lymphoma 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 Hodgkin Lymphoma.
  • 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 Hodgkin Lymphoma 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: four cases from St. Michael, 2 cases from Northwestern and one case from Stratford Central. There is nothing to indicate that these high schools are different from other high schools in Ontario. The increase in Hodgkin Lymphoma in Perth County began before the new St. Michael school was constructed.
  • None reported having had mononucleosis, which has been associated with Hodgkin Lymphoma.

Next Steps

Following this investigation, the Health Unit will continue to work with Cancer Care Ontario to monitor the rates of Hodgkin Lymphoma 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 Hodgkin Lymphoma continues to be an uncommon illness and the number of Perth County youth affected is small,” says Dr. Miriam Klassen, Acting Medical Officer of Health.

Ontario Health Study

The Perth District Health Unit is encouraging residents to join the Ontario Health Study. 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.

What is Hodgkin Lymphoma?

  • Lymphomas are cancers that begin in the immune system. The cause of Hodgkin Lymphoma is not fully understood, but one specific virus (Epstein-Barr Virus), genetic factors and environmental factors have been identified as possible causes. Hodgkin Lymphoma is not contagious.
  • Hodgkin lymphoma can cause many symptoms:
    • Swollen lymph nodes (that do not hurt) in the neck, underarms, or groin
    • Weight loss for no known reason
    • Fever that does not go away
    • Soaking night sweats
    • Itchy skin
    • Coughing, trouble breathing, or chest pain
    • Weakness and tiredness that don’t go away

Most often, these symptoms are not due to cancer. Infections or other health problems may also cause these symptoms. Anyone with symptoms that last more than two weeks should see a doctor so that problems can be diagnosed and treated.

More Information

For a copy of the complete report, please call Health Line at 519-271-7600 or toll-free at 1-877-271-7348 extension 267.