September 24, 2017
How Slums Affect Health
Expert Q&A

How Slums Affect Health

by Jeanine Barone  |  

lee rileyLee Riley, MD, is a professor of epidemiology and infectious diseases at the University of California, Berkeley. He and a colleague, Jason Corburn, recently published Slum Health: From the Cell to the Street, a book that looks at the health of the urban poor living in slums around the world.

There's a political movement underway in the U.S. against globalization, with proponents believing that isolationism keeps the problems (including health problems) of people in the slums out of our backyards. But all the while there are people living in slums right here in the U.S., where there are serious health issues. Can you address this?

The best example would be what’s going on with the Zika virus. We now have transmission in Miami. For that to begin in Miami, someone would have had to go to another country and bring it back, where it started its own local epidemic. There’s no way to restrict infectious diseases. They have no borders. Infectious diseases spread with movement of people and with the globalization of food products. So it’s not just “their problem.” It’s our problem. The unanswered question is that Zika has been known since the 1940s; it has been smoldering in Africa for many years. Suddenly when it entered South America it became an epidemic. Why? In Brazil, for the first time, Zika entered large urban communities with densely packed settlements. These conditions allowed for rapid and high transmission of the virus. When this epidemic exploded in the slums, it spread everywhere else. Tourists from upper-income North America go to these cities and they get infected, whether they’re in a slum or not. Everything is connected. It’s the same with Ebola. Until three years ago, it appeared as small outbreaks in rural Africa, and then exploded in West Africa, where it entered large urban slum communities. Several Americans got infected. There’s no way people can ignore what’s going on in these communities.

India has more antibiotic-resistant strains of bacteria than almost anywhere else in the world. How does the slum situation there play a role, and how does it impact the health of people in developed countries?

India is a reservoir of drug-resistant infectious organisms. It’s because of the Indian health system. There’s no universal national health insurance system. But there’s high-quality health care for the people who can afford it. For people with no resources, the system is not adequate. In the slums, there are government-run clinics, but the people don’t trust them or don’t have access to them. So they go to private clinics and private pharmacies that are not regulated, and get antibiotics without a prescription. So people are misusing antibiotics. Lower-income people are then more likely to acquire drug-resistant infections.

It’s not just the use of antibiotics in people. India is becoming wealthy. As nations get richer, they demand more protein-based food. So you need more animals that need antibiotics for growth promotion. This selects for drug resistance. So it’s a double whammy. A glaring example is British people flying to India, Pakistan, and Southeast Asia for medical tourism. It’s very affordable. They end up back in the U.K. with a drug-resistant infection and this spreads to others in Britain.

This year’s summer Olympics in Rio brought attention to the favelas (Brazilian slums) in that city. What's the health situation like in those slums?

They have infectious diseases that usually don’t spill over into other communities. One example is leptospirosis, a bacterial disease transmitted through rat urine. It’s found in certain types of favelas in valleys that are prone to flooding. The urine mixes with the floodwaters and the people walk through the waters and become exposed. Favelas on the hills don’t flood. But they do have diarrheal diseases, caused by organisms such as E. coli and Salmonella, because it’s difficult to transport water up the hills. So the people tap into the city water system—for example, connecting a plastic water pipe to a city-supplied metal water pipe. Such connections could get contaminated because the plastic pipe may break or is not connected to the metal pipe correctly. These plastic pipes could be submerged in contaminated water and pathogens can seep into the illegal pipes.

How big of a problem is the health of people living in slums, and how does this differ from what we find in the developed world?

We are studying this, but many of these communities are not recognized by governments. We are going into these communities to assess disease burden (the number of cases of the disease). We know from India that they have different types of slums. The government officially recognizes some but not others. Which means births and deaths are not recorded in some slums. These are invisible populations. We have done work in Brazil, and in Rio we divided the city into slums vs. non-slums. We know that tuberculosis (TB) occurs in much younger people with higher mortality rates in slums than in non-slums, where it occurs more in older people. But among people 15 to 30 years old, the number of reported TB cases was lower in the slums. Why? Most of the people in that age group were in jail. So there’s no data on the population. People in slums, especially kids under 5 years old, if they get TB, 100 percent die, because the diagnosis isn't done quickly. So they’re not counted either. They don't make it to the surveillance system.

Is this problem stagnant or going in a positive direction?

It varies from country to country. Brazil is one of the leaders in dealing with slums. They are now trying to improve conditions, such as giving land tenure rights to the people where they live. If the people have ownership, they sometimes behave differently and try to improve their conditions.

What's the single most important takeaway message you can give to readers, based on your research?

Everyone should recognize that many cities in the world, including the U.S., have people living in slums. These communities and populations need to be recognized. You can’t just ignore them or their people. The health of a whole city or a nation depends on the health of all the subpopulations in that city or nation, because drug-resistant infectious diseases do not have any social, economic, ethnic, or physical barriers.

This opinion does not necessarily reflect the views of the UC Berkeley School of Public Health or of the Editorial Board at

Also see How Housing Affects Health.