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Public  Health
“Prevention is better than cure”


Many people think about medical services in terms of a visit to the doctor followed by a course of drugs or an admission to a hospital. This is reactive medical care, an attempt to provide a “magic bullet” to cure a disease or condition already being suffered by the patient. Out of sight and largely out of the mind of the layman is another whole branch of medicine, normally termed Public Health. Professionals working in the realms of Public Health concern themselves with whole populations rather than individuals, their core speciality being the prevention and control of epidemics.

On this web page CIRCLIST explores this proactive world of preventative medicine, firstly as a matter of generality and then with specific reference to the subject of male circumcision as a means of curbing the spread of sexually transmitted infections.



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What is an Epidemic?

In common speech the word epidemic refers to the sudden spread of a disease, as manifested by its symptoms. Only when someone falls ill do we tend to think of them as infected. This is misleading, because it is entirely possible for someone to be either a benign carrier of a particular illness or in the incubation period (sometimes‒especially when lengthy‒called the latency period), the time period between becoming infected and the onset of symptoms.

Professionals studying epidemics need to adopt a somewhat more strict approach. In Public Health terms, a person is infected as soon as they acquire the disease, even if they are symptomless and even if they have not yet reached the stage of being able to pass the infection to others. Throughout the rest of this web page, the terms epidemic and infected are used with this strict academic meaning.



Why do epidemics grow and shrink?

Here comes rule number one of the science of epidemiology, the study of epidemics:
Any epidemic grows if the average infected person passes their infection to more than one other individual. Conversely, any epidemic declines if the average infected person passes their infection to less than one other individual.
The measure of natural, unimpeded transmission is properly termed the Basic Reproduction Value, R0. A high value means that the number of cases will increase rapidly in the absence of intervention, whereas a number less than 1 means that the outbreak of infection is destined to fade away naturally.

In Public Health terms, a course of remedial action is worthwhile if it significantly reduces actual transmission below the natural value of R0. Ideally one would wish to see transmission reduced to zero. Do that and the epidemic is halted in its tracks. But we are dealing with practicalities, not with ideals. Any reduction is beneficial; potential remedies must not be cast aside just because they are not 100% effective. In the world of applied epidemiology, partially effective remedies have a very meaningful role to play.

Real progress has been made once an epidemic is tipped from growth into decline, but that isn’t the end of the story. Adding further preventative measures, further reducing actual transmission, continues to be beneficial to society at large because the epidemic will then shrink faster. Some people will still become infected, but the numbers of new infections will be reduced.



Can an epidemic die out altogether?

Yes. This happens when the pathogen (the organism or substance causing the disease) runs out of new hosts. There are a number of ways in which such an absence of new hosts can be engineered:

  • Physical Quarantine.

    This involves incarcerating all infective persons and their recent contacts in a place away from all uninfected persons. Such isolation needs to last until the progress of the disease in the infected individuals has passed the point where they are capable of infecting others. Put bluntly, this involves either recovery or death. In contacts who do not develop the infection, isolation must be maintained for a length of time exceeding the incubation period. The technique has been used for centuries, especially in respect of travellers carrying smallpox, but it is only practical in respect of diseases with a relatively short incubation period and amongst populations with low mobility, otherwise the number of “recent contacts” becomes unmanageable.
Quarantine Notice (19,512 bytes)
An interesting ethical dilemma arises in respect of placing in quarantine an asymptomatic carrier - a person who carries the disease, is capable of infecting others, but shows no symptoms and thus appears to be fit and well. The classic example is Typhoid Mary, Mary Mallon (1869–1938), who worked as a cook in various locations in New York State, USA. An asymptomatic carrier of Typhoid Fever, she is known to have infected 53 people three of whom died.

Where does the boundary lie between an individual’s right to freedom and society’s right to protection from infection? This is a recurrent question in Public Health and, as we shall see, not a matter confined to the issue of quarantine.


  • Drug-simulated Quarantine.

    This is something relatively new. In respect of certain virally-transmitted diseases, it is now possible to reduce the infectiousness of a sufferer to near-zero, such that their presence amongst the uninfected population is of no consequence. An example is the use of the drug Acyclovir to reduce the infectivity of cases of Shingles (Herpes Zoster caused by the varicella-zoster virus). In this scenario the anti-viral drug does not kill the virus but works by stopping the virus from multiplying. With no new viruses being dispersed from the rash and its associated skin lesions, the condition ceases to be highly infective.
Acyclovir (19,512 bytes)
Is the same true in respect of sexually-transmitted viral infections?

Well yes, up to a point. In May 2011 it was realised that early intervention with anti-retroviral drug treatment reduces the risk of transmission of HIV from an infected partner to an uninfected one by a staggering 96%.

Unfortunately, though, the situation isn’t as simple as it is with Shingles. When HIV is the pathogen at issue, one is dealing with a latency period that can last for years. This raises the question "How do you tell the difference between a symptomless carrier and an uninfected person?". Tests do exist, but they are expensive and time-consuming. Also expensive are the anti-retroviral drugs needed to 'quarantine' those found to be infected. So the idea, whilst it works in theory, does not yet seem to have the makings of a workable Public Health campaign even in the context of the single issue of HIV.

  • Local barriers.
We have all seen newsreel footage of folk wearing face masks during influenza epidemics. That’s an example of a local barrier. In the realm of sexually transmitted diseases, the equivalent is the condom.
Facemask (23,269 bytes) Condom (17,191 bytes)
Both influenza and the common cold are spread by droplets expelled when an infected person breathes out, speaks, spits, coughs, splutters or sneezes. The face mask prevents many of these droplets reaching other people and thus reduces the probability of the infection being spread. In the case of sexually transmitted diseases, the condom performs a similar role. Body fluids from one person are prevented from reaching someone else, along with the bacterial or viral payload they contain. The nature of the barrier is different, but the principle is the same.

  • Induced Immunity.
Around since the advent of smallpox innoculation, deliberately induced immunity equips the body to cope with an attack of the real disease should it occur. The principle behind immunisation involves issuing an advance warning to the body’s immune system, priming it to react rapidly and appropriately if the real disease appears, so preventing the infection from establishing itself in the new host.
Smallpox vaccination (109,767 bytes)

As a precaution against biological warfare, the US
Navy continues to vaccinate against smallpox even
though the pathogen is extinct amongst civilians.

Influenza innoculation (21,641 bytes)

In many developed countries, influenza vaccines
are offered annually to the elderly and those
with compromised immune systems.

Vaccines against sexually transmitted infections have proved difficult to devise. A vaccine does now exist for HPV, the pathogen responsible for most cases of cervical cancer, but it is not 100% efficacious and on the evidence to date it does not provide a constant level of protection for life. Furthermore, it only protects against some strains of HPV - not all. Modern society has tended to place great reliance on vaccination programmes to the exclusion of other preventative health measures, despite the high cost of vaccine development and deployment.

The difficulties of vaccine deployment are too frequently ignored. Leaving aside accidental laboratory infections, the last case of smallpox was reported in Somalia in 1977. For the first time ever, a major disease had been completely vanquished. Dr H.Mahler, WHO director-general at the time, described the smallpox program as “a triumph of management, not of medicine”. It is said that at a meeting in Kenya in 1978 Donald Henderson, who had directed the smallpox program, was asked which disease was next in line to be eradicated. Henderson reached for the microphone and said that the next disease that needed to be eradicated was bad management (Hopkins, 1989).

For there to be any prospect of total eradication by vaccination, a pathogen must not have any reservoir in the environment or in wild animals. In other circumstances, the best that vaccination can achieve is protection, containment and control.

Mass vaccination campaigns again raise the question of the balance between rights of the individual and the reasonable expectations of society at large. All vaccines carry risk, a fact acknowledged by the creation of compensation payment schemes for those deemed to have been vaccine-damaged. A leading example of such a scheme is that currently existing in the United Kingdom. The history of the UK compensation scheme is well summarised on the website of the Association of Parents of Vaccine Damaged Children, which has onward links to the UK Government’s web pages relating to eligibility and claims.


  • Acquired immunity.

    Some (but only some) diseases that are not normally fatal can only be caught once. An example is Chicken Pox. If everyone in a community has already had Chicken Pox, an epidemic of it will die out simply because there are no more individuals for the pathogen to infect. Even in the twenty-first century it is commonplace for mothers to arrange Chicken Pox Parties for children, in effect deliberately infecting their offspring with the disease in the justified belief that it is less serious to suffer as a child than as an adult. Not applicable to sexually transmitted diseases, though. None of the relevant pathogens trigger acquired immunity, so forget the idea of a justified teenage orgy!
Chicken Pox Party invitation (35,059 bytes)



The mathematics of partial protection (simplified version)

Partial protection works principally because its effect is cumulative. Compare the following sequences. In each case, we start with a group of 16 newly infected individuals and explore the consequence of these people being ‘at large’ in the general population.

First, for the sake of example, let’s assume that each infected person, on average, infects two others. Following the course of the epidemic through four transmissions of the infection we find:
New infections:16 > 32 > 64 > 128 > 256
Patient total:16 > 48 > 112 > 240 > 496
Now let’s try that again, having introduced a Public Health measure that halves the number of transmissions per infected person. So we are now looking at the case where each infected person, on average, only infects one other person rather than two.
New infections:16 > 16 > 16 > 16 > 16
Patient total:16 > 32 > 48 > 64 > 80
After four cycles of transmission, our single imperfect solution to the problem has reduced the number of patients from 496 to 80. Progress, but nothing like a cure.

Now let’s introduce a second, independent form of prophylaxis. Still imperfect, but again better than nothing. Say the new form of prophylaxis again halves the number of transmissions per existing infected individual. The picture then becomes:
New infections:16 > 8 > 4 > 2 > 1
Patient total:16 > 24 > 28 > 30 > 31
That still leaves 31 people somewhere out there suffering the consequences of being infected. So we do not have a cure. What we do have is an epidemic that is heading towards the point where Herd Immunity kicks in.



The concept of Herd Immunity

It might at first sight appear that, in order to extinguish an epidemic, it is necessary to confer immunity on every individual in the population. Not so. Remember that an epidemic dies out when the pathogen runs out of new hosts. For a new infection to occur, it is not sufficient for there merely to be a non-immune individual ‘somewhere out there’. The mathematical laws of probability come into this. As an epidemic declines, a point is reached where the probability of a new infection occurring drops significantly due to the rarity of an infectious person coming into contact with a non-immune potential host.

The point at which the rarity issue becomes significant is the point at which “herd immunity” is said to commence. Reach that point (typically somewhere around 85% to 95% of the population immune, depending on the infectivity of the disease) and there is a reasonable prospect that the epidemic will be defeated without the need to track down and individually protect the remaining non-immune individuals.

In scenarios involving vaccines, herd immunity is particularly significant in protecting those individuals who cannot be vaccinated either due to an allergic reaction to a component of the vaccine or a compromised immune system.



Circumcision as a Public Health issue

It has been demonstrated to accepted standards of scientific proof that circumcision reduces the transmission rate of a considerable number of sexually-transmitted infections (STIs). The cost to society of cures (where available), palliative treatment, social security costs, economic losses and so on is considerable. STIs have long been regarded as a valid public health issue. Now that the prophylactic effects of male circumcision have been quantified, a case can be made for increasing circumcision rates worldwide.

The World Health Organsiation is promoting the procedure in countries with high rates of HIV-1 infection. But what about elsewhere? Why wait for an epidemic of any one of the relevant diseases before taking action? Why not act on a pre-emptive basis?

At this point it is helpful to consider male circumcision as a surgical vaccination. The analogy is not a flight of fancy; circumcision has the following in common with many vaccines: but circumcision has the additional benefits: The analogy breaks down when one considers the mechanism by which protection is achieved. Vaccinations prime the immune system in readiness for an encounter with the real pathogen, clearly not the case with circumcision. No matter. What is of interest here is the result rather than the means by which it is achieved.

Would a campaign of male circumcision in, say, Europe be asking too much? We hear much nowadays about the rights of the individual within society, rather less about the responsibilities of the individual towards the rest of society. The very concept of public health calls that balance into question; inherent in the concept is the notion that the individual owes a duty to society in respect of infection control. When it comes to vaccinations, most people accept the obligation. A few ‘refuseniks’ exist, but their numbers are insufficient to destroy herd immunity.

The state, for its part, might usefully extend the surgical vaccine analogy by setting up a compensation scheme for individuals whose circumcisions proved to be less that satisfactory. Once in place, it would seem reasonable for the state to both facilitate and promote circumcision not only in terms of personal health and hygiene but also as part of a citizen’s obligation towards the common good, as it does with immunisations.

In respect of public health generally, perhaps we all need to pause and remind ourselves of this quotation from the inaugural address of U.S. President John F. Kennedy, Friday, January 20, 1961, words that are etched in stone at his gravesite in Arlington National Cemetery:

Ask not what your country can do for you; ask what you can do for your country.




Acknowledgements

The following resources were used in the preparation of this web page:
USA flag US Navy Seal (14,553 bytes) Public Domain photo library of the United States Navy.
Image ID: 021219-N-5297M-001.jpg dated December 2002.
USA flag Westview Press logo (7427 bytes) Hopkins, JW. 1989. The Eradication of Smallpox: Organizational Learning and Innovation in International Health. Boulder, CO: Westview Press.
USA flag National Library of Medicine logo (1988 bytes) New England Journal of Medicine logo (15,705 bytes) Celum, C. et al., 2010. Acyclovir and Transmission of HIV-1 from Persons Infected with HIV-1 and HSV-2, New England Journal of Medicine 362: 427–439. [Pubmed abstract]
UK flag Website of the Association of Parents of Vaccine Damaged Children, edited by Rosemary Fox MBE.




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