There’s no question about it; H1N1 is sweeping through Ontario, and has been for a few weeks now. You’ve probably already heard that Ontario government has released the vaccine, and is dispensing it across the province. I would strongly encourage you to consider getting yourself vaccinated.

Most of my readers are young, and mostly healthy. As such, the need to protect yourself from flu is not pressing. If you contracted H1N1 today, it would likely only mean missing a few days of school or work. So why get vaccinated? Because the flu pandemic is spread by droplet contact from person-to-person. Vaccinate yourself so that you’re not just another person in the long line of transmission. Because that line ends with people who are more susceptible, and who are going to die from it. Vaccinate yourself on behalf of Ontario’s elderly, the immunosuppressed patient who uses the pay-phone after you, the pregnant woman next to you on the bus, and the cancer patient. Getting the H1N1 vaccine is the socially responsible thing to do.

Find an Ontario vaccination clinic near you at this website. Vaccination schedules will vary by region, and in most regions where there are limited supplies of the vaccine, you will be prioritized according to your risk. First to be vaccinated are those in danger themselves, and second those who have susceptible close contacts (e.g. health care workers). If neither of those are you, be prepared to wait a bit for your vaccine. Keep checking back, however, because eventually there should be enough for everyone.

There have been rumours and anxiety going around about the safety of the vaccine. As always, be discerning about where you get your information. Those organizations most-equipped to assess the quality of the H1N1 vaccine have pronounced it safe, and effective. In general, vaccines are the safest medications around. That being said, the vaccine is likely to give you a sore muscle at the injection site, and perhaps a headache, fever, and flu-like symptoms for a day or two. This is not the flu, but rather your body’s immune system responding. Take Tylenol for your symptoms, and you shouldn’t be held back. Ultimately, a day or two of headache, and a sore shoulder are far better than having the flu itself, which can last more than a week!

Do it for your grandparents, for your nieces and nephews, and for the many Ontarians depending on you to do your part. Get your flu vaccine.

Every year internationally, 1.5 million children die from diarrheal dehydration. That’s more children dying than the total number of Canadian children under 5 years old. What’s truly tragic is how preventable these deaths really are. In studying today, I ran across a set of guidelines published by the WHO for case management of diarrhea:

1. Prevent dehydration by educating parents on how to treat diarrhea at home (fluids, and good nutrition)
2. When dehydration occurs, treat with oral rehydration solution.
3. Feed appropriately both during and after diarrhea.
4. Provide antibiotics for suspected cholera, shigella dysentary, or typhoid fever.

It has been estimated that these four guidelines could prevent 90% of deaths from diarrhea dehydration. That’s 1.35 million children. So simple (no special training required for the first three guidelines, and the fourth can be performed by just about any healthcare worker), yet the barriers are numerous. Some obvious barriers are the lack of access to clean water for rehydration and inability to pay for good nutrition.

Many of you will have heard on the news about the recent spread of a new Influenza outbreak from Mexico. Some have probably been wondering “what’s the big deal?” With 59 deaths reported by the WHO as of April 23, and less than 1000 cases of swine flu, this disease is, so far, a small player. So I’ll do my best to explain why this disease is getting infectious disease experts stirring, and why it will be one to keep a watchful eye on over the next few days and weeks.

From the days of the Ancient Greeks, the Influenza virus has infected people. But the genetic identity of the Influenza virus today isn’t the same as for the virus that caused the flu 100 years ago. In fact, it’s not even exactly the same virus as it was last year. The reason is that the Influenza virus mutates rapidly, generating new strains.

From year to year, the changes in the Influenza virus are known as genetic drift. Because of genetic drift, each flu season there are a new handful of Influenza strains that predominate. Genetic drift explains why you have to get a new flu shot every year. In the Fall, the WHO makes predictions of which five strains of Influenza they think will be the most prevalent, and those are the strains that go into the vaccine.

In addition to genetic drift, every so often there is a more significant mutation in the Influenza virus. We classify Influenza strains according to two proteins that are expressed on the virus capsules: hemmaglutinin (H) and neuroaminidase (N). For example, H5N1 is the subtype name for a strain of bird flu that is being watched globally for pandemic potential. The recent swine flu in Mexico is H1N1. Genetic drift from year to year doesn’t generally change the HxNx classification of the virus, and so over time the world population builds up some immunity to strains that are prevalent.

Every once and awhile, however, there is a chance recombination of the virus that results in a new subtype becoming infectious in humans. Often these recombinations come from animal strains of the flu, because animals suffer from different subtypes than we do. Many animal flu strains can be transmitted to people, but generally you need to have contact with the infected animal, and it won’t spread from person to person. If an animal flu recombines, however, to be transmissible from human-to-human, it might potentially create a new subtype to which we have no global immunity. This sets the stage for a global pandemic. Over history there have been regular, periodic pandemics of newly recombined Influenza strains the most notable being the Spanish Flu, which killed 40% of the global population.

Perhaps now it is clearer why there is so much fuss over the emerging swine flu epidemic. Swine flu has existed in pigs for forever, and there was always pig-to-human transmission. The new event, is that this H1N1 strain of swine flu has recombined to be infectious from human-to-human. It now fits the criteria for what we expect a pandemic-causing virus to look like. Will swine flu be the cause of the next Influenza pandemic? That will depend on many factors including the transmissibility and virulence of the virus itself, and how effectively it is contained by WHO efforts. It will be a disease to keep a very watchful eye on over the next few days and weeks.

(DISCLAIMER: This post is a little more technical, and hopefully will be enjoyed by my dear friends in math, engineering, or computer science).

Let:

R° = the average number of secondary cases infected by each person who has an STI (units: people)

β = the percentage probability that a person with an STI will spread the infection to a current susceptible sexual partner.

c = the average number of new sexual partners made (units: people/month)

D = the average duration of infectiousness for a particular STI (units: months)

M = the average number of people with an STI cured from infectiousness each month by medical intervention (units: people/month)

The change in prevalence of an STI in the population is determined by R°:
- If R° < 1, the STI is declining in prevalence
- If R° = 1, the STI is in equilibrium
- If R° > 1, the STI is becoming more prevalent 

R° can be expressed in terms of the other variables: 
     R° = βcD

Given a particular M, and noticing that β and D are constant for each STI, R° varies with c. Studies of sexual practices show that c follows a Poisson distribution that is heavily skewed towards the left. Thus:
- In most populations (the left-skew of the distribution), c is low enough that R° < 1
- There exist “core” populations (the right-sided tail of the distribution) where c is high enough that R° > 1. 
- Demonstrated core populations are: young people, sex-trade workers, and drug users.
- By estimating β and D, we can determine the threshold c for which R° = 1 (c = 1 / βD), and above which there is increasing prevalence of the STI. 

Some interesting research findings regarding core groups and epidemics:
- Like-with-like sexual activity (= within a core group) is a risk factor for a fast-developing, but limited STI epidemic.
- When core groups are small enough, there is self-limiting of the epidemic since sexual contacts become very likely to have previously contracted the infection
- Like-with-unlike sexual activity (= between a core group member and non-core group member) is a risk factor for a slow-developing, but ultimately more prevalent epidemic. 

STI prevention focuses on:
- Increasing M, which causes a decrease in D
- Advocating safe-sex and protective behaviours that reduce β
- Identifying core groups for focused medical attention and STI screening

Whoever said that mathematicians have no hope of ever becoming familiar with sex ? Course this isn’t quite the type of familiar I think they were hoping for…

I’d like to put forward a lego-ethical question raised during our symposium on HIV/AIDS today. It’s a complex question, and one that I certainly haven’t found an answer for that I’m comfortable with. But here are two contrasting arguments for consideration.

The question was whether or not people living with HIV should be legally obligated to inform their sexual partners of their HIV status.

R. v Cuerrier:

In 1998 the Supreme Court of Canada convicted Henry Cuerrier guilty of sexual assault for having unprotected sex with two women without informing them that he knew he was HIV-positive. Neither of the women actually contracted the virus. I’m mostly legally-illiterate, but as far as I understand it, the court’s rationale went something like this:

Cuerrier was guilty because he knowingly jeopardized the lives of the two women. Although in both cases the women consented to the sex, the prosecutor made a successful argument that their consent was vitiated (nullified) on the basis of fraud. Since Cuerrier had failed to disclose his status, their consent was made with incomplete or fraudulent information. 

Reactions:

Many see the criminalization of non-disclosure of HIV-status as an over-extreme means to address the spread of HIV, which is more-appropriately a public health issue. Read through (only 2 pages – it’s worth it!) this position paper disseminated in June 2008 by the Ontario Working Group on Criminal Law and HIV Exposure.

One of our patient-lecturers this morning expressed his view that criminalization has done worse for the spread of HIV than it has helped. That’s because it has made people even less willing to get themselves tested. Undeniably, the law does not take into consideration the complex array of factors that play into a person’s ability to disclose including limited knowledge about the virus, social stigma, and discrimination.

Does Protection Change the Question?

During unprotected intercourse, there is a 0.2-0.5% risk of HIV transmission from someone who is infected i.e. the risk is small, but real. Using protection such as a condom takes this small risk and vastly reduces it further. Of course, condoms are not fool-proof, and the risk is never zero. But should using protection make a difference for the duty to disclose?

Some say yes. Since the quantity of risk matters, using protection might arguably make HIV transmission pass from the category of a “foreseeable consequence” to “unforseeable”, thus eliminating the duty to disclose.

Your thoughts?

And now, for an intriguing (but horrible) story:

Mary Mallon was an Irish cook who moved to New York City in the year 1900. Only 31-years-old at the time, Mary took up employment in a wealthy man’s home preparing meals for the family.  Sadly however, within a couple of weeks the entire family became very ill. Concerned, Mary soon found another family to work for. It wasn’t long after though that Mary’s new family started falling sick as well. Some became severely affected, and the laundress of the household was overcome and passed away. So Mary moved again, this time to the home of a lawyer. Sure enough a few weeks later, the lawyer and most his family were sick in bed. Mary did her best to care for them, but finally she moved to yet another household.

George Soper, a typhoid researcher, eventually caught up with Mary and heard about her succession of failed employments. George had a theory that he put forward to Mary; he suggested that she might be the very first reported case of a typhoid carrier – that is, someone who can spread the disease without personally suffering from it. Mary was adament that she wasn’t carrying typhoid, and proceeded to infect three more households. In fairness, the Irish were never treated very well in New York City, and Mary may have had good reason to be suspicious of George’s accusations.

Mary was eventually apprehended and taken into custody by the city’s public health department. She was held in quarantine for some time before the city released her on the condition that she change her occupation from cooking to something less conducive for spreading infection! Mary agreed, but later changed her name to Mary Brown so that she could resume her work as a cook. She infected two more households! Eventually Mary was apprehended again and, sadly, held in quarantine for the rest of her life.

Typhoid fever is a disease that results from the bacteria Salmonella enterica typhi. It causes severe, inflammatory gastroenteritis resulting in bloody diarrhea and rapid fluid loss. Before widespread use of antibiotics, it was a fatal disease. Many of Mary’s victims died. Salmonella enterica typhi are spread by fecal-oral transmission. Likely in Mary’s case, bacteria in her fecal matter contaminated her hands, and then as a result of poor hand hygiene were transferred to her clients via the food that she prepared.

In Lewis Carroll’s ‘Alice’s Adventures in Wonderland’, there occurs a race between Alice and the Red Queen. Like everything else in Wonderland, there’s something unusual about this race! It takes place on the spot. Alice and the Red Queen sprint at the fastest speed that they possibly can, but they don’t seem to get anywhere. This confuses Alice at first, but the Red Queen explains it:

“It takes all the running you can do, to keep in the same place.”

The symbolic meaning of this story led Matt Ridley to name a famous hypothesis in evolutionary biology after it: the Red Queen hypothesis. Simply stated, the Red Queen hypothesis claims that species must evolve at the maximum rate possible just to avoid extinction.

In class on Friday, our microbiology professor provided a fabulous example of the Red Queen hypothesis at work. It has to do with the bacteria Staphylococcus aureus, which is a normal member of the skin flora and is presumably living comfortably on you at this moment! S. aureus can infect wounds, however, and it’s important that we have some effective antibiotics against it.

Penicillin used to work against S. aureus in the 1950’s. Then we used it far too much. Inevitably, the bugs gained widespread immunity, and today penicillin is completely ineffective against S. aureus. So in the 1980’s we began using methicillin instead. Unfortunately (but predictably) this led to the evolution of methicillin-resistant S. aureus (MRSA), which is now a nightmarish perpetrator of hospital-bourne infections. Vancomycin was the next tool in our antibiotic arsenal, but in 2002 we began to see vancomycin resistant S. aureus.

So the race continues between bacteria and antibiotic – both “running” as fast as they can but neither quite getting anywhere.

Every year on December 1st, physicians across Canada donate their day’s salaries towards HIV/AIDS treatment and prevention. As medical students we don’t have a salary to donate yet, but we do have time! So today, despite being in a state of grasping for every spare minute to study for our upcoming exams, lots of us took some time today to hear a couple of speakers. One was an infectious disease specialist who works on HIV/AIDS treatment in Kingston, and the other was the director of a Kingston community program.

I learned a few things that I wanted to share!

First, HIV/AIDS is a Canadian issue! That may be bleedingly obvious to some people, but if you’re anything like me then you tend to think of AIDS as a worldwide problem, where “worldwide” means not here. The reality is that AIDS is very present in our Canadian communities. While I should certainly continue thinking about AIDS on a global level, this realization encouraged me to re-think what I can potentially do to fight AIDS. Fighting may consist of sending money overseas and raising awareness of the pandemic, but it may also involve getting more personally involved with AIDS here in Canada.

The second thing I learned is more political. I had no idea, but apparently our current Conservative government has made it abundantly clear that they will not financially support any HIV/AIDS programs that have a “harm reduction” element. Harm reduction was new terminology for me: basically it means making it safer for people to engage in behaviours that they will be doing anyway, instead of trying to change those behaviours. Condom distribution and needle exchanges are two examples of harm reduction strategies that have had meaningful, well-documented success.

From a clinical perspective, there is no alternative to harm reduction! As doctors, we have no right to say what anybody should be doing with their lives. But, we do have the responsibility to advise people about risky behaviour and offer them the tools to protect themselves.

I’m disappointed that our government hasn’t recognized the seriousness of HIV/AIDS in Canada. Instead of looking at the evidence, which says beyond any doubt that harm reduction saves lives, they have reduced a tangled social problem into an absolute moral maxim that lacks relevancy in the complexity of the “real world”.

Anyway, I’d love to hear about anything you learned on World AIDS Day 2008! Post a comment and keep the conversation going!