BC physicians should be aware of the risk of waterborne infection in the province, particularly for immune-compromised individuals in communities with inadequately treated water supplies.

Cryptosporidium infection is of particular concern since it can cause severe disease in immune-compromised individuals and is not inactivated with chlorine. Conditions that in­crease the risk of severe Crypto­sporidium infection include:

• HIV infection with a CD4+ count of < 100 cells/mm3.
• Hematological malignancies (lymphoma or leukemia) under active treatment or in remission and off treatment for less than 1 year.
• Hematopoietic stem cell transplants.
• Primary immunodeficiencies that affect the number or function of CD4 cells, IFN-gamma and CD40 ligand such as severe combined immunodeficiency (SCID), selective IgA and Saccharomyces opsonin deficiencies, hyper-IgM syndrome and gamma-IFN deficiency

Individuals with the conditions listed above should consider the following additional drinking water treatments:

• Boiling. If the water supply is disinfected with chorine, simply bring water to a full boil. If the water supply is not disinfected with chlorine, filtered, or UV treated, boil for at least 1 minute (2 minutes at elevations >2000m).
• Filters. Filters used should be labeled as “Absolute” (1 micron or smaller), meeting ANSI/NSF International Standard #53. Jug-type filters and some built-in devices are not effective.
• Reverse osmosis.
• Ultraviolet treatment. Treatment must meet NSF Standard #55A.
• Bottled water. Check with company that water has been adequately treated.

Patients can be referred to HealthLink BC File #56, “Drinking Water and Those with Weakened Immune Systems” at www.healthlinkbc.ca/healthfiles/hfile56.stm [10]. For more in­formation on the treatment of the local water system, contact your drinking water supplier or the drinking water officer in your health authority.
—Perry Kendall, MBBS
Provincial Health Officer