The fight against disease

By the dawn of the 1900s, advances in medicine allowed doctors to step up the battle against the diseases that have plagued humankind, particularly communicable diseases such as diphtheria, typhoid fever and scarlet fever.

The struggle to eradicate these microscopic menaces was not easy. As late as 1929, a public health report noted an epidemic of typhoid fever in Ontario and more than 400 cases of diphtheria across the country. Even the dreaded smallpox was still a threat, with 200 cases reported in Canada in 1928.

With the vaccines available today thanks to medical and drug research, such diseases are now almost non-existent. Canadian children are inoculated against polio, tetanus, diphtheria, measles, rubella, mumps and pertussis (whooping cough) while vaccination for hepatitis B is mandatory for all children when first entering school in Canada. Moreover, public health authorities routinely advise Canadians to be vaccinated against several other diseases such as influenza type B.

However, even as some of the older threats to human health have been controlled, new or different infectious diseases are emerging to challenge modern medicine and our public health system as never before. For example, the SARS (Severe Acute Respiratory Syndrome) outbreak in 2003 originated in China and then spread to Canada and other nations around the world. SARS is a respiratory illness caused by a previously unknown type of corona virus. Normally, corona viruses cause mild to moderate upper respiratory symptoms, such as the common cold. But SARS is new, so there are still many questions unanswered questions about this often deadly illness.

During the 1980s and 1990s, human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS) emerged as a worldwide health concern. AIDS is caused by HIV. From 1985 to 2003, over 55,000 Canadians were reported to be diagnosed with HIV. Due to improved treatment, the median time from HIV infection to AIDS diagnosis now exceeds 10 years and people are living longer with AIDS; however, AIDS is fatal and there is no cure.

Since the mid-1980s, the pattern of HIV/AIDS infection has changed significantly in Canada. At that time, the disease mostly affected men who had sex with men. However, the proportion of women with HIV has increased considerably in the last decade. In 2003, women accounted for 25.3% of positive reports among adults, an increase from 8.9% in the period from 1985 to 1993. At the same time, the proportion of adult positive HIV test reports attributed to injecting drug use has gradually declined to 11.8% in 2003 from a high of 33.7% in 1996.

Men who have sex with men continue to account for the largest number and proportion of positive HIV test reports. This proportion decreased from close to 75% in the period from 1985 to 1994. In the mid- to late- 1990s, the proportion dropped and remained close to 37% until there was a slight increase to 44.4% in the years from 2000 to 2003. The diverse heterosexual exposure category has steadily increased from 7.5% before 1995 to 36.9% in 2003.

In 2002, men who had sex with men accounted for 41.5% of positive HIV tests, an increase from 36.1% in 2001. Heterosexual  exposure accounted for 29.9% of positive HIV tests in 2002, from 32.6% in 2001. This represented a dramatic climb from 9.1% from 1985 to 1996.

An infectious virus that is carried in the blood like HIV is hepatitis C, a disease that affects approximately 240,000 Canadians. The number of people with hepatitis C is increasing rapidly in Canada and around the world, primarily among those sharing needles and other drug equipment.

Although the hepatitis C virus has existed for a long time, it was only identified in 1989. Of the more than 5,000 newly infected Canadians each year, up to 70% experience no symptoms. For some, symptoms may not appear for 20 or 30 years. Approximately 15 to 20 percent of people infected recover from the infection. However, the majority progress to a chronic infection. The course of the disease in the chronic phase is slow and may last a lifetime. Up to 20% of those infected develop cirrhosis, which severely damages the liver. A smaller percentage develop liver cancer.

Tuberculosis (TB) is another serious communicable disease. When the cure for tuberculosis was discovered in 1948, doctors were optimistic that the disease could be eradicated by 2000. Although Canada has one of the lowest tuberculosis rates in the world, TB continues to be a concern.

However, not all groups of Canadians are equally at risk. Immigrants from countries where TB is common accounted for 62% of the 1,704 new cases seen in Canada in 2001. Canadian-born Aboriginal people are also at higher risk. They have an infection rate of 24.3 per 100,000 people, whereas Canadian-born non-Aboriginals have a rate of 1.1. Moreover, 2001 marked the first time that the proportion of cases among Canadian-born Aboriginals surpassed the proportion among Canadian-born non-Aboriginals (18% and 16% respectively). In Nunavut, 97% of TB cases occurred in the Aboriginal population, where the infection rate was 47.5 per 100,000 people.

Diseases formerly regarded as exclusively tropical are also finding their way to Canada. The incidence of imported malaria in Canada has increased steadily since the early 1990s. Malaria remains an important concern for travellers returning from tropical regions, and this disease accounts for illness and deaths in Canadian travellers. There appears to be a cyclical pattern of imported malaria, with notable peaks occurring every four to five years (1986/87, 1991/92 and 1996/97). During the last peak, in 1997, there were 1,029 malaria cases reported in Canada; a 65% decrease was seen the following year with only 368 cases reported. In 2000, fewer than 400 malaria cases were reported.