Infectious diseases, also known as communicable diseases, are those that can spread from an infected person, animal, or object to another person, potentially making others ill. It has been estimated that each year in Ontario, there are more than 7,000,000 infectious disease episodes and approximately 4,900 deaths.1 Across Canada, the direct (e.g., hospitalization costs) and indirect (e.g., lost productivity) costs associated with infectious diseases was estimated at $8.3 billion in a single year.2
Many different pathogens can cause infectious disease. In Ontario, public health units have a mandate to “reduce the burden of communicable diseases and other infectious diseases of public health significance”.3 In order to achieve this mandate, the Health Protection and Promotion Act (HPPA) requires that all regulated health professionals and laboratories report certain infectious diseases that are considered to be of public health significance. Public health units follow up all infectious disease cases reported according to the HPPA in order to prevent other people in the community from becoming ill, and to detect when outbreaks of these diseases may be emerging.
In this topic, the diseases that are reported to public health units under the HPPA are grouped into the following seven categories:
| Sexually transmitted and blood-borne infections | Chancroid, Chlamydia, Gonorrhea, Hepatitis B, Hepatitis C, HIV/AIDS, Syphilis (all types) |
| Respiratory infections | Blastomycosis, Influenza, Legionellosis, Severe Acute Respiratory Syndrome, Tuberculosis (active) |
| Enteric infections | Amebiasis, Botulism, Campylobacteriosis, Cholera, Cryptosporidiosis, Cyclosporiasis, Giardiasis, Hepatitis A, Listeriosis, Paralytic shellfish poisoning, Paratyphoid fever, Salmonellosis, Shigellosis, Typhoid fever, Verotoxin producing E. Coli (VTEC) |
| Infections prevented by routine immunization | Diphtheria, Haemophilus influenzae type b (Hib) (invasive), Measles, Meningococcal disease (invasive), Mumps, Pertussis (whooping cough), Polio, Rubella, Rubella (congenital syndrome), Streptococcus pneumoniae (invasive), Tetanus, Varicella (chickenpox) (hospitalized), |
| Vector-borne infections | Lyme disease, West Nile virus |
| Zoonotic infections | Anthrax, Brucellosis, Echinococccus multilocularis infection, Hantavirus pulmonary syndrome, Plague, Psittacosis/Ornithosis, Q fever, Rabies, Trichinosis, Tularemia |
| Other infectious diseases of public health significance | Acute flaccid paralysis, Carbapenemase-producing Enterobacteriaceae (CPE), Cholera, Creutzfeldt-Jakob disease (all types), Encephalitis/Meningitis, Group A streptococcal disease (invasive), Group B streptococcal disease (neonatal), Hemorrhagic fevers, Leprosy, Ophthalmia neonatorum, Smallpox |
Between 2005 and 2018, sexually transmitted and blood-borne infections (STBBIs) were the most common infectious diseases among Middlesex-London residents, accounting for 73% of all cases reported. During this 14-year time period, the numbers and corresponding rates of all reportable STBBIs consistently increased, regardless of the specific infection.
Chlamydia infections were the most common STBBI reported between 2005 and 2018, followed by hepatitis C infections. Rates of both these infections were consistently higher than Ontario rates; the local incidence of all other STBBIs was comparable to or lower than provincial rates. Although case counts were comparatively low, syphilis infections increased nearly five-fold across the 14-year time period, which was the greatest increase among all STBBIs.
At-risk groups for STBBIs varied depending on the infection. In Middlesex-London, rates of chlamydia, gonorrhea, and hepatitis C infections were highest among youth and young adults between the ages of 15 and 29 years of age. For gonorrhea, hepatitis C, HIV/AIDS, and syphilis, the local rate among males was higher than the rate among females; a portion of this difference may be associated with cases among men who have sex with men. Finally, the use of injection drugs was reported by 70.3% of HIV/AIDS cases between 2014 and 2018. People who use drugs (PWUD) were an at-risk group for other STBBIs as well, including hepatitis C.
In the 14-year period from 2005 to 2018, approximately 12% of all infectious diseases reported among Middlesex-London residents were respiratory infections. Influenza was the most common respiratory infection reported, with more than 4,000 cases reported in across the entire time period. Local influenza rates were highest among those 60 years of age and over, and among infants under the age of one year. In the most recent three years, the rate of influenza infections among Middlesex-London residents was significantly higher than in Ontario.
Compared to influenza, other respiratory infections were characterized by much lower incidence. The rate of active tuberculosis cases among Middlesex-London residents varied between 2005 and 2018, with the highest rates among those in their 20s. Across the 14-year time frame, the rate of legionellosis infections among Middlesex-London residents increased, with those 60 years of age and over characterized by the highest rates. Local rates of both active tuberculosis and legionellosis were comparable to or lower than rates across Ontario as a whole.
From 2005 to 2018, enteric infections represented approximately 11% of infectious diseases reported among Middlesex-London residents. Campylobacteriosis was the most common enteric infection reported across the entire time period, followed by salmonellosis. Enteric infections varied seasonally, with the average number of reported cases generally highest in the summer months of June, July, and August.
Age groups most at risk for enteric infections varied depending on the disease. For cryptosporidiosis, giardiasis, salmonellosis, and verotoxin-producing Escherichia coli (E. coli) (VTEC), rates among Middlesex-London residents were highest among children under the age of 10 years. In contrast, local incidence rates of campylobacteriosis, cyclosporiasis, hepatitis A, and shigellosis were highest among adults in their 20s or 30s.
Patterns of reported enteric infections also varied year over year. The rates of cryptosporidiosis and cyclosporiasis among Middlesex-London residents generally increased between 2005 and 2018, although some of this increase might be due to changes in laboratory methods. Local rates of amebiasis and VTEC decreased across the same time frame. All other enteric infections varied, with no obvious increasing or decreasing patterns. Between 2005 and 2018, enteric infections rates among Middlesex-London residents were similar to or lower than Ontario rates, with the exception of amebiasis infections, for which the local rate exceeded the provincial rate in the most recent five years.
Among Middlesex-London residents, most vaccine preventable diseases, such as measles, invasive meningococcal disease, mumps, polio, rubella, and tetanus, were rare or were characterized by low incidence between 2005 and 2018. However, pertussis (whooping cough) infections continued to be reported, and local rates were comparable to or lower than the rate in Ontario. Among Middlesex-London residents, the incidence of pertussis was highest among infants less than one year of age, followed by children 1-9 years of age.
Cases of invasive Streptococcus pneumoniae, another vaccine preventable disease, were also reported between 2005 and 2018. The rate among Middlesex-London residents was comparable to or lower than the Ontario rate, and those 60 years of age and over were characterized by the highest incidence rate.
Between 2005 and 2018, the number of reportable vector-borne infections identified among Middlesex-London residents was low, at fewer than 100 in total. However, local counts and rates of both Lyme and West Nile virus infections increased over the 14-year time frame. The rate of Lyme disease cases among Middlesex-London residents was generally lower than the provincial rate, while the local and provincial rates of West Nile virus infections were comparable between 2005 and 2018.
Zoonotic infections, such as human cases of anthrax, hantavirus, plague, and rabies were rare among Middlesex-London residents between 2005 and 2018. For brucellosis and Q fever, fewer than 10 cases were reported for each disease across the 14-year time period, corresponding to very low local incidence of these infections.
Most other infectious diseases of public health significance, such as acute flaccid paralysis, Creutzfeldt-Jakob disease, and hemorrhagic fevers, were rare in Middlesex-London. One exception was invasive group A streptococcus disease. A local outbreak of this infection emerged in 2016, and the incidence rate among Middlesex-London residents exceeded the Ontario rate between 2016 and 2018. At-risk groups for this outbreak included PWUD and people experiencing homelessness.4
Infectious diseases represent a substantial burden of illness in the Middlesex-London region. Ongoing efforts are needed to not only monitor for emerging clusters of cases, but to also inform public health actions to sustain progress where declining rates have been achieved, to reduce the occurrence of other higher-incidence infections, and to target efforts to at-risk populations.
References:
1. Kwong JC, Crowcroft NS, Campitelli MA, Ratnasingham S, Daneman N, Deeks SL, Manuel DG. Ontario burden of infectious disease study (ONBOIDS): an OAHPP/ICES report [Internet]. Toronto (ON): Ontario Agency for Health Protection and Promotion, Institute for Clinical Evaluative Sciences; 2010 [cited 2019 Apr 8]. 198 p. Available from: https://www.publichealthontario.ca/-/media/documents/onboid-ices.pdf?la=en
2. Diener A, Dugas J. Inequality-related economic burden of communicable diseases in Canada. Can Commun Dis Rep [Internet]. 2016 Feb 18 [cited 2019 May 24];42(Suppl 1):S7-13. Available from: https://doi.org/10.14745/ccdr.v42is1a02
3. Ontario Ministry of Health and Long-Term Care. Ontario public health standards: requirements for programs, services, and accountability [Internet]. Toronto (ON): Queen’s Printer for Ontario; 2018 Jan 1 [revised 2018 Jul 1; cited 2019 Feb 12]. 75 p. Available from: http://www.health.gov.on.ca/en/pro/programs/publichealth/oph_standards
4. Dickson C, Pham MT, Nguyen V, Broacher C, Silverman MS, Khaled K, Hovhannisyan G. Community outbreak of invasive group A streptococcus infection in Ontario, Canada. Can Commun Dis Rep [Internet]. 2018 Jul 5 [cited 2019 May 31];44(7/8):182-8. https://doi.org/10.14745/ccdr.v44i78a06
Last modified on: July 25, 2019