Population density and disease

Written for a housing policy forum. Part 8

Sanitation in Shakespeare’s London
Woodcut from ShakespearesEngland.co.uk.

The advantages of high population densities

Urbanists literature shows that higher density living brings many social and economic advantages. In 5 Key Themes Emerging From the ‘New Science of Cities’, Michael Mehaffy says:

Cities generate economic growth through networks of proximity, casual encounters and “economic spillovers.” The phenomenal creativity and prosperity of cities like New York is now understood as a dynamic interaction between web-like networks of individuals who exchange knowledge and information about creative ideas and opportunities. Many of these interactions are casual, and occur in networks of public and semi-public spaces—the urban web of sidewalks, plazas, and cafes. More formal and electronic connections supplement, but do not replace, this primary network of spatial exchange.

A later section will discuss the ‘New Science of Cities’, Smart Cities and ‘networks of ‘proximity’.

Population density is an important aspect but there are, of course, constraining factors. Part 7, Pollution in Towns, discussed the impact of the air pollution caused by traffic in denser urban areas. This section will discuss the spread of disease.

The problem of disease and population density

In Infectious Diseases and Human Population History, Andrew P. Dobson and E. Robin Carper write:

Epidemiological theory suggests that host population density is critical in determining whether a pathogen can become established and remain endemic in a population.

But simple density is not the only driver . In As cities grow more crammed and connected, how will we discourage the spread of disease?, Nate Berg writes:

“Before, when Ebola would pop up in an isolated village, it wouldn’t spread so much. But now the areas are so large, they’re so interconnected,” says Emily Blodget, a specialist in infectious disease at the University of Southern California. “Because of the urbanization of those areas we’ve had outbreaks. and the amount of people that have been affected is just so much more.”

Rates of disease are also affected by lifestyles and living conditions. The Worst Diseases in Shakespeare’s London in Shakespeare Online describes the public health of London at that time:

Shakespeare’s overcrowded, rat-infested, sexually promiscuous London, with raw sewage flowing in the Thames, was the hub for the nastiest diseases known to mankind.

The Building Centre’s Beyond the Green Belt, describes the attempts of Queen Elizabeth I to deal with this problem in 1593 This was to prohibit the expansion of London:

No new buildings shall be erected within three miles of London or Westminster. One dwelling-house in London, Westminster or three miles thereof, shall not be converted into more.

Public Health Solutions

Density and travel set two contributory factors in the spread of disease but good practice in sanitation helps. The outbreak of Legionnaires disease was first identified at the 1976 at the American Legion convention in Philadelphia. Changes to the maintenance of air-conditioning and hot water tanks quickly followed – backed by legislation.

In 1854, John Snow, one of the fathers of modern epidemiology, famously traced the source of a cholera outbreak in Soho, London. He was born in York in 1813 in North Street.

At 14 Snow was apprenticed to a surgeon in Newcastle upon Tyne where he first encountered cholera, which entered Newcastle via the seaport of Sunderland in 1831. During this epidemic victims were buried outside York City walls just round the corner from where Snow was born.

Later, in London, he found that the cause of the Soho cholera cluster was infected water from one pump. This was related to the density of population, in that there were many families within a water-carrying distance of the infected pump, but the cause was infected water from one pump. The local council took the simple public health measure of removing the handle to the pump. This probably stopped the outbreak.

Good sanitation can be provided even where population density is very high: Modern cities do not have a problem with cholera.However, clean water is not available in many parts of the world, but cholera does occur in modern refugee situations, particularly where population densities are high, as in the Rohingya crisis:

The incredibly high population density in the camps and high levels of severe malnutrition among child refugees both increase the risks associated with an outbreak of acute watery diarrhoea and cholera. In the last week, 5011 cases of diarrhoea have been reported.

Despite other public health remedies like vaccination and antibiotics, Dobson and Carper warn:

While medical and sanitation technology have certainly helped minimize the impact of infectious diseases in the last two centuries, humans can only really claim victory over one pathogen – the smallpox virus. It seems inevitable that other diseases (e.g. measles and typhus) that may now be simmering quietly in scattered populations will reemerge as the susceptible subpopulations of major cities increase to threshold sizes.

Nate Berg also reports Emily Blodget’s assessment of travel and urbanisation:

Blodget says the risks of urbanization are closely interrelated with globalization, which has made it relatively easy for someone who’s unknowingly carrying Zika, Ebola or countless other diseases to get on a plane and land in a densely packed city. The SARS outbreak in Hong Kong in the early 2000s was blamed not only on density but also on the high rate of people traveling into and out of the city, according to Blodget.

Blodget recognises that international travel can increase infection rates, which are more worrying for dense populations. The arrival of an infection in a large, dense city puts a greater number of people at risk – and more quickly. In a similar sized population spread over a larger area the infection progresses more slowly and with good public health actions will not infect so many.

Antibiotics and vaccines

Increased travel makes the spread of diseases easier at a time when we have The Antibiotic Resistance Crisis:

From the late 1960s through the early 1980s, the pharmaceutical industry introduced many new antibiotics to solve the resistance problem, but after that the antibiotic pipeline began to dry up and fewer new drugs were introduced. As a result, in 2015, many decades after the first patients were treated with antibiotics, bacterial infections have again become a threat.

There is also the struggle to keep vaccines up-to-date. On this flu season, The Telegraph reports:

In the teeth of one of the deadliest flu seasons in several years, scientists have already placed a bet on how to tackle the virus next winter.

Late last month, the World Health Organisation (WHO) identified the flu strains it believes the public will need protecting from next year. It ordered large drug companies to develop vaccines to match up.

… and the South China Post says ‘Another flu pandemic is coming, and the world isn’t prepared‘.

Postscript. Bio-terrorism

In Biothreats Are Exploding. Firewalls And Fallout Shelters Won’t Help, Loren Thompson writes:

A case in point occurred recently, when scientists at the University of Alberta synthesized horsepox virus, and then published a paper explaining how they did it. Publishing research findings and methods is standard practice in the life sciences, but in this case the scientists were disclosing how to fashion a virus very similar to that which caused smallpox.

Smallpox is one of the most infectious diseases known to man. It has killed hundreds of millions. The World Health Organization succeeded in eradicating the virus during the 1970s. But because it no longer is present in nature, vaccine production has largely ceased and resistance to the disease has diminished. So if it were to appear again in engineered form, the consequences could be horrendous.

Very worrying. I have written on Planning for terrorism before – also to be addressed in later sections.