What’s infecting us?

In the long run, our odds of death are 100%. But what’s going to kill us? I really like this nice graphic from National Geographic, using stats from the US National Safety Council, which illustrates the big killers.


I find this graphic fascinating. Of course it doesn’t include every way to go – just some of the most and least common ways. It would be fascinating to see how this graphic has changed over time. Consider this:

In 1931, humans could fly across oceans and communicate instantaneously around the world. They studied quantum physics and practiced psychoanalysis, suffered mass advertising, got stuck in traffic jams, talked on the phone, erected skyscrapers, and worried about their weight. In Western nations people were cynical and ironic, greedy and thrill-happy, in love with movies and jazz, and enamored of all things new; they were, in most senses, thoroughly modern. But in at least one important way, they had advanced little more than prehistoric humans: They were almost helpless in the face of bacterial infections.

That’s from the superb The Demon Under the Microscope, which describes the invention of sulfa drugs in the late 1930’s. Much has changed since that time. What killed us then can now be treated with a routine course of antibiotics. And tremendous progress has been made at defeating (or at least controlling) viral and fungal infections, too. Yet in terms of health care burden, infectious disease still causes a lot of illness. Where I’m located, in Ontario with a population of 13 million, there are over 7 million episodes of infectious disease every  year, and 5000 die. So what’s still causing all this sickness? And what can the death-averse do about it?

A recent paper on societal burden of infectious disease in Ontario answers some of these questions. Researchers quantified the burden of different infections using health-adjusted life years, factoring in years-of-life-lost as well as years of reduced functioning. Statistics on disease prevalence were gathered from different health  care databases. They applied this methodology from mild infections right through serious illnesses. The final report ranks 51 different infectious diseases. Here are the biggest:

The Ten Most Burdensome Illnesses

#1. Hepatitis C Virus (HCV)

Hepatitis C causes liver hepatitis (inflammation) and is transmitted mainly by blood-to-blood contact (e.g., shared needles). Many do not have symptoms, and the disease can be latent for years or even decades. In some it causes liver scarring, fibrosis, and cancer. In Ontario it kills almost 400 per year. There are medications that can be helpful, but HCV is still the most common cause of liver transplant.

Vaccine? No

Preventable? Don’t share needles. Injectable drug use is the most common cause of HCV.

#2. Streptococcus pneumoniae

S. pneumoniae is a bacteria and the most common cause of pneumonia and meningitis. Mild infections can mean ear and sinus infections. In Ontario this means 500,000 illnesses and over 600 deaths per year. Found among the normal respiratory tract bacteria, it typically does not cause problems in adults except in cases where immunity is compromised.

Vaccine? Yes. A vaccine against 23 types of S. pneumoniae is available for adults. Children receive Prevnar, which protects against 80-90% of severe S. pneumoniae infections.

Preventable? Yes, the best prevention is by vaccine. The vaccine has dramatically reduced infections in children.

#3. Human Papillomavirus (HPV)

HPV is a common sexually-transmitted virus that can cause cervical, anal, and head and neck cancers. It has the greatest impact of all sexually-transmitted infections. In Ontario it causes over 1000 cases of cancer per year, resulting in over 250 deaths. It also causes over 14,000 new cases of genital warts per year. HPV infections are common, about half of sexually active men and women become infected at some point in their lives. There are no treatments or cures for the virus itself.

Vaccine: Yes! Versions are now available (e.g., Gardasil) that protect against some of the forms of HPV that can cause cancer. In Ontario, a universal program for girls means all female children are offered the vaccine.

Preventable: Yes, HPV is sexually transmitted. Condoms can reduce the risk of transmission but are not 100% effective at blocking transmission. The Pap smear is used to identify abnormal cells in the cervix before they can progress to cervical cancer.

#4 Hepatitis B Virus (HBV)

HBV infects the liver, and may cause symptoms. However, infected infants can go on to develop chronic hepatitis, with some progressing to cancer. This is much less common in infected adults. HBV also causes liver cirrhosis and liver cancer. Over 300 die per year in Ontario.

Vaccine? Yes! In Ontario a school-based program ensures all children are vaccinated.

Preventable? Yes. HBV is transmitted by sexual contact, injectable drug use, and from mother to child during childbirth or breastfeeding.

#5. Escherichia coli (E. coli)

E. coli is ubiquitous in our environment and particularly in our gastrointestinal tract. If it escapes, it can cause bladder, kidney, and bloodstream infections. It’s a very common infection, infecting over 450,000 per year, and killing 600.

Vaccine? No

Preventable? Hygiene can help prevent infections.

#6. Human Inmmunodeficiency Virus (HIV)

HIV causes AIDS, and is transmitted by sexual contact, needle sharing, exposure to HIV-contaminated fluids, and mother to child during childbirth/breastfeeding. Innovative treatments for HIV have totally transformed the disease from a death sentence to more of a chronic disease. It infects over 1600 per year in Ontario, killing 133.

Vaccine? A vaccine remains elusive.

Preventable? Yes, with proper precautions.

#7. Staphylococcus aureus

S. aureus lives without causing problems in much of the population. However it can also cause a range of infections, particularly in hospitalized patients. Outside hospitals, it causes skin, bone, joint, heart and lung infections. The hard-to treat methicillin-resistant S. aureus (MRSA) is a significant problem in hospitals, where it can easily be spread from patient-to-patient. S. aureus infects over 150,000 per year, killing over 250.

Vaccine? No

Preventable? This is mainly an issue for hospitals, where good infection control processes can block transmission.

#8. Influenza

Influenza is a viral infection that I’ve blogged about before. It causes seasonal epidemics, peaking in the winter in the northern hemisphere. Most infections mean severe fatigue and muscle pain for several days. More severe cases mean ear infections, bronchitis, and pneumonia. In Ontario, there are over 600,000 infections per year, killing almost 300.

Vaccine? Vaccines exist, though due to antigenic drift, must be repeated annually. Ontario offers a universal program to all residents.

Preventable? To some extent the risk of influenza infection can be reduced through hygiene measure. Supplements like echinacea and ginseng have not been shown to be effective. Wash your hands, and get the vaccine.

#9. Clostridium difficile (C. difficile)

C. difficile (“C diff”) s a bacteria that causes gastrointestinal infections, especially in situations where normal bacteria have been disrupted in some way (e.g., antibiotics). Very common in hospitals, can be difficult to treat, and it kills about 1 in 20 of those infected. In Ontario there are over 5000 cases per year, killing 167.

Vaccine? None

Preventable? C. difficile infections can be prevented through proper infection control processes. Minimizing unnecessary antibiotics is important as well.

#9. Rhinoviruses (The common cold)
Rounding out the list is the lowly rhinovirus, cause of the common cold that infects over 1.6 million per year and a few deaths each year. Rhinoviruses are spread via droplet (sneezing) and contaminated objects (watch those doorknobs).

Vaccine? None

Preventable? As per influenza, the best approach is to maintain good hand hygiene. Over-the-counter remedies can provide relief of symptoms, but will not affect the underlying infection. Supplements like Cold-fX or Flu Shield have not been shown to be effective.


The burden of infectious disease ranges from the common, mild and short-duration (e.g., rhinovirus infections) to acutely severe (meningitis) through controllable, chronic infections (e.g., hepatitis or HIV). Looking over the list, a number of interventions like vaccines have been introduced, and for other, known control measures (e.g., hygiene) exist. Importantly, some of the most serious infections are largely restricted to hospitals and other health care settings. Interestingly, there’s probably little public awareness of the burden of the different diseases. I suspect that most would assume HIV kills more than HPV, when the opposite is the case.

What’s notable by their absence are the illnesses that have largely been eliminated by vaccination: measles, mumps, rubella, tetanus, polio and diptheria. Keeping immunization rates high is critical to maintain herd immunity and keep these infections from recurring.

On balance, the odds of severe illness or death from infectious disease seem very low for the vast majority of people. That’s a reassuring finding, and we should marvel at the science that has conquered, controlled, and even prevented our biggest killers.

2 thoughts on “What’s infecting us?

  1. Well, I agree that vaccines are important, but the value of the 23-valent pneumococcal vaccine is not agreed on by all. The Cochrane review of the 23-valent vacine suggested that while it may be protective against IPD, all-cause pneumonia and death remain unchanged. I’m a bit undecided about this vaccine; it has good protection in the groups that need it the least, poor protection in the groups that need it the most, and little effect on overall deaths, suggesting that the protection against IPD isn’t that valuable.

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