Pandemics are defined as large-scale outbreaks of an infectious disease that can vastly increase morbidity (occurrence of disease) and mortality over a wide geographic area.  Inevitably, pandemics cause significant economic, social, and political disruption. Most pandemics in history have originated through “zoonosis’, the transmission of pathogens from animals to humans. The bubonic plague of the 6th century (rats), the 1918 ‘spanish flu’ (pigs) now known as H1N1, SARS or Severe Acute Respiratory Syndrome (birds) known as H5N2 and H5N2, and finally COVID 19, which probably had its genesis in the wild animal consumption market in Wuhan, China. Presently 75% of emerging infectious diseases are of animal origin. We don’t know how exactly they spill over into humans, except in the case of pigs (with their remarkable physiological similarities to humans) who can catch both avian and human flu viruses. 

Two terms that are relevant to the understanding of pandemics are spark risk (where a pandemic is likely to arise) and spread risk (how likely it is to disperse through human populations). 

• Spark risk is present in high levels in West and Central Africa, South and Southeast Asia and China - regions that have experienced rapid expansions in human settlements, intensive agricultural and livestock production, and increased exploitation of natural resources. Such factors create greater contact between humans and animals that amplify pandemic risks. 
• Spread risk may be due to disparate factors: high rates of global travel in Europe and America, poor investment in response infrastructure, and slow uncoordinated responses.

While most seasonal flu viruses bind only to the upper respiratory tract (nasal passages, sinuses, larynx and pharynx), this virus also binds to the lower respiratory tract (trachea, bronchial passages and air sacs in the lungs).  Viruses that bind to the lower respiratory tract target, infect and inflame the lungs.  This makes COVID 19 potentially more deadly since it can result in pneumonia, an infection that scars the lungs allowing them to fill with fluid and/or pus.  Upper respiratory tract viruses spread easily due to coughs and sneezes but the chances of a patient developing pneumonia are lower. COVID 19 does both - it can spread easily and cause pneumonia.  

Whether the reason for this wildfire spread of COVID 19 is a highly virulent disease, our urban living or our global travel, there is no question the virus is exceptionally contagious. Whatever the reason, we seem to think that the strides in medical technology will blunt the spread of disease. But when it is a novel virus that none of our immune systems have encountered before - there are no antibodies built up in our systems, no herd immunity (resistance within a population resulting from a number of individuals being immune to the disease, through vaccination or prior exposure) and no immediate treatment, hence leading to the rapid spread and high morbidity rates.

A Brief History of Pandemics and Outbreaks

The bubonic plague impacted the Byzantine Empire (Eastern Roman empire) during the reign of Justinian in 541–542 AD. It was caused by a bacteria pathogen known as Yersinia Pestis carried by rats on grain ships, transferred to humans via fleas as the intermediate host.  At the height of the outbreak, 5,000 people died per day and by the time the plague had run its course, as many 100 million people, half the population of Europe, had perished.

‘The Black Death,” the recurrence of the plague in 1347, was ignited by ships docked at the port of Messina in Sicily and spread rapidly to kill one-third to half the population of Europe within a few years. The Venetians banned sailors from entering their cities for 30 days, which they later extended to 40. The Italian term “quaranta giorni” (literally, “40 days”) is the root of the English word “quarantine.” 

The 1918-1919 flu pandemic was a particularly virulent strain of what has recently been called the H1N1 influenza virus A or swine flu, because people who originally caught it had direct contact with pigs. Spread by soldiers returning from WWI, the pandemic killed approximately 50 million worldwide, including about 675,000 Americans. The U.S. government’s response to the 1918 pandemic was eerily similar to that of the current White House to COVID-19, where officials at first downplayed the threat with disastrous results. 

The SARS (Severe Acute Respiratory Syndrome) outbreak of the early 2000s, also known as H5N1/H5N2 or avian flu, in Hong Kong is known to have been passed from birds and bats to humans. It was blamed not only on density but also on the high rate of people traveling into and out of the city. During November 2002 through July 2003, a total of 8,098 people worldwide became sick and of these, 774 died.

The Ebola virus outbreak in West Africa in 2014 may have been linked to bats or nonhuman primates (chimpanzees, apes, monkeys, etc.) It showed that it is not just major cities that are vulnerable but what matters for infectious diseases is the availability of pathways for travel, even if it’s from village to village. The death toll stands at 11,232, with 28,646 Ebola cases. 

COVID 19 was declared a pandemic by the Word Health Organization (WHO) as of March 11, 2020.

How Pandemics Shape Cities: Public Health Policy and Urban Planning

Cities have existed since about 10,000 years ago. The advent of agriculture which allowed for humankind to build up stores of food, also allowed people to settle down and give up the nomadic life in exchange for a more sedentary, settled existence. Small settlements gradually expanded, ultimately becoming what we call cities.  Resources could be easily shared as urban centers reduced transport costs for goods by bringing them all together in one spot. The physical density of people gave energy to these large settlements and the results were increased specialization and productivity along with innovations in many fields. 

Unfortunately, pathogens could also be shared and sanitation issues were the biggest reason for disease outbreaks in the early history of cities.  Empires and nation building further facilitated the spread of diseases, which traveled along trade and commerce routes. As humankind figured out how to manage water distribution and sewage, sanitation overhauls helped reduce the risks. What is clear is that the earliest cities had one striking characteristic in common with the market in Wuhan, ground zero of the coronavirus outbreak: humans lived in close proximity with animals.

During the cholera outbreaks of the 1800s, Americans learned that when infected water pooled in meandering, unpaved streets, diseases could spread more easily. Subsequently, it was understood that cities organized on grids are more than just convenient, they are conducive to public health - straighter streets can better accommodate long pipes underneath to safely move water and waste. 

As tuberculosis ravaged the U.S. at the turn of the 20th century, public parks, such as the Emerald Necklace in Boston and Central Park in New York City, became popular. Soon after that, there was a tremendous push to design buildings and outdoor areas that brought in fresh air and sunlight as these were seen to be remedial for certain diseases. Tuberculosis had a valuable influence on architecture and urban planning up to about the 1960s, especially in modern public housing. There is no denying that crowded urban areas are uniquely vulnerable to public health crises, especially, as the percentage of the world’s population living in urban areas will increase from 50% in 2008 to 70% in 2025. 

However, there are actions that can be taken to counteract the role of cities in spreading disease - transparency, public information and engagement (beyond medical professionals, awareness must percolate through all aspects of daily life), and collaboration between private and public sectors. The switch to working remotely, using webinars instead of conferences and video-chats instead of meetings is a step in the right direction. With these tools at our disposal, we don’t necessarily need the physical density that at first could only be provided by cities - the digital world can provide the same kind of energy without the risk.

How Pandemics are Spread: Globalization and Air Travel

Today, the far-reaching issue for pandemics is more about globalization and less about urban settlements.  Rapid global air travel is a relatively recent phenomenon and was not as important a factor till the 1950s and 60s.  Before that travelers went by sea (with many a disease outbreak on ocean liners) and even when they went by plane, there were not the numbers of travelers that we see today. In 2017 the International Civil Aviation Organization (ICAO) documented a record-breaking 4.1 billion people taking to the skies compared to just a few million passengers in the 1950s.

The present volume of global travel is a sizable factor in spreading disease. Important to note is it may not just be from city to city - not everyone who arrives at an airport stays in the city. They may be continuing on to the suburbs or another urban center, either way passing through new areas. Hence diseases can bypass large cities and spread directly to other lower density towns. As a result, even the best prepared city, with the cleanest infrastructure, can still be vulnerable to outbreaks.

Safety protocols in global travel are crucial to controlling the spread of disease. Airport operations can be augmented to include disease detection and prevention, with robust surveillance and response systems. Airports can be likened to something like the firewalls that a computer uses to prevent viruses - fever checks to catch people with symptoms before they can enter the city.  The fact that Covid 19 is on every continent except Antarctica shows us that it isn’t just cities that are the problem, but it is global pathways due to worldwide travel and the frequency with which these are used. 

Cities and the resulting density can spread disease within that population but cities are not the reason it is spreading from continent to continent. High speed modern travel now aids the spread of a pandemic across the planet in the same way urban planning and public transport facilitated it across cities. The problem, however, is in our reactions - our mindset has yet to catch up with this, and until it does, the virus will always be a step ahead of us.