Urbanization and Slums Infectious Diseases in the Built Environment: Proceedings of a Workshop (2018) / Chapter Skim
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3 Understanding Infectious Disease Transmission in Urban Built Environments
3 Understanding Infectious Disease Transmission in Urban Built Environments
Pages 17-34
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From page 17... ...
David Smith, professor of global health at the University of Washington, explored the migration and movement of pathogens through pathways within, into, and out of urban centers, highlighting a project that mapped the transmission of malaria using cellular phone data in Kenya. THE INFLUENCE OF SLUMS ON POPULATION HEALTH AND MICROBIAL COMMUNITIES Framing the issues surrounding slum health, Lee Riley, professor and head of the Infectious Diseases and Vaccinology Division at the University of California, Berkeley, noted that the topic has been on the table for more than a decade, ever since the United Nations Human Settlements Programme (UN-Habitat)
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From page 18... ...
He said that residents of both areas are affected by infectious diseases, including tuberculosis (TB) , HIV/AIDS, sexually transmitted infections, influenza, sepsis, urinary tract infections, hospital infections, and pharyngitis.
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From page 19... ...
He said that suboptimal schools are associated with poor health education and poor nutrition; he added that undernutrition and obesity are associated with infectious disease outcomes. He reported that inappropriate and inadequate health services both contribute to poor vaccine coverage, maternal health complications, underutilization of health services, rheumatic heart disease, suicide, drugresistant TB, and chronic diseases, such as hypertension and diabetes.
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From page 20... ...
Riley reported that the diversity index for the isolates from the children who attended the private clinic was 0.92, which is almost identical to the diversity index for high-income countries according to a systematic review of global emm type distribution (Steer et al., 2009)
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From page 21... ...
in Salvador, Brazil. NOTE: Orange bars are isolates that are included in the 26-valent experimental vaccine for group A Streptococcus; purple bars are isolates that are not included.
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From page 22... ...
Zika Virus Disease Riley touched on Zika virus infection and its congenital consequences to illustrate another case of how slum conditions, such as overcrowding, inadequate safe water supply, and poor quality housing, can drive high levels of virus transmission. Mosquitoes that thrive in communities living in overcrowded conditions increase the risk of human infection, he explained, so people living in slums are more likely to be exposed to diverse virus populations than people who live in more affluent, less overcrowded areas.
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From page 23... ...
During the severe acute respiratory syndrome (SARS) nosocomial outbreak in Hong Kong in 2003, Li and his colleagues suggested that the virus transmission was airborne, at least for that particular outbreak (Li et al., 2005)
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From page 24... ...
A surgical mask can help prevent transmission of large droplets in close contact, he said, but neither general ventilation nor surgical masks can prevent close-contact airborne transmission (less than 1.5 meters)
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From page 25... ...
He noted that the fomite route may be easier to separate, but there is not a way to do it yet. He reported that there are no field data on indoor air networks and surface touch networks, although some data on closecontact networks have been captured.
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From page 26... ...
PATHWAYS OF PATHOGEN TRANSMISSION IN URBAN CENTERS David Smith, professor of global health at the University of Washington, explored several pathways through which pathogens can be transmitted within, into, and out of urban centers. He noted humans in particular generally carry cell phones with them when they move around, enabling measurement of how often and how far people move.
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From page 27... ...
He explained that around 12,000 cell towers are scattered across Kenya, with most of the users being served by a single cell phone company that facilitated the data collection. He described how the investigators mapped the country's urban areas, densely inhabited buffer settlements surrounding urban areas, and cell tower locations, and then assigned each region a relative risk for malaria.
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From page 28... ...
He added that Nairobi has had anopheline vectors in the past as evidenced by massive malaria epidemics at the end of the previous century, so transmission is possible in Nairobi. Shifting Vector Transmission in the Built Environment Smith explained that there are global patterns of shifting vector transmission in urban built environments.
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From page 29... ...
This is because of a global pattern in which cities tend to lose their anopheline vectors as they develop, he explained, but the anophelines tend to get replaced by Aedes aegypti mosquitos that can thrive in urban centers. This catalyzes a shift in the built environment away from malaria and toward dengue and arboviral transmission, which is a mounting problem in urban centers around the world.
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From page 30... ...
He added that lack of access to water for hand washing has been studied in the context of children under 5 years of age contracting respiratory infections in their homes. Riley added that he collaborates with people who do this type of work in slums, such as one researcher who studies indoor air pollution caused by cooking with biofuels in rural areas and now is applying this work to slums, but more researchers are needed.
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From page 31... ...
Riley added that interpersonal injuries are major contributors to health outcomes, noting that his studies comparing TB burden in slum and nonslum communities found that the DALY gap was reversed among young adult males in Rio de Janeiro (that is, the DALY was higher among the nonslum community young adult males) (Marlow et al., 2015)
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From page 32... ...
Edward You, supervisory special agent in the Federal Bureau of Investigation's Weapons of Mass Destruction Directorate, raised the issue of modern urbanization contributing to an increasingly controlled environment in which people are more immunologically naïve, which, in turn, drives increased incidence of diseases like obesity and asthma. While the focus is often on disease transmission and pathogens perturbing the system, he wondered whether the controlled environment may also be setting populations up for failure in the future.
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From page 33... ...
Riley said he has a dark vision of the future and predicted that the issues faced by urban slums will get much worse before they improve; he said that the effect of slums on global health will be evident long before the effects of climate change and did not envision any concrete, immediate solutions. Li took a more optimistic stance, predicting that humans will be smart enough to find those solutions and create better urban centers.
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From page 34... ...
He suggested finding ways to improve slum conditions for those people, when there is often government resistance to improving infrastructure and living conditions in slums that is premised on keeping people living there from becoming permanent residents. Sands asked if there are any good models for low-cost ways to absorb large numbers of relatively poor people into a dense urban environment.
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