No connection. Before the intervention, toilets in many homes did not tie into the sewer system.
CREDIT: PATRICIA BORJA
Feces happen. And when millions of people live in the same city, a lot of it happens every day; and if it isn't properly disposed of, the health of the population goes down the toilet.Throughout the world, more than 2 billion people lack proper sanitation, which is integrally tied to water supply for both personal hygiene and sewage systems. In all, 1.6 million children die each year from related diarrheal diseases, making it the third leading cause of mortality in children under age 15 in middle- and low-income countries. "Third World cities have a huge internal environmental problem created by fecal contamination that needs to be solved," says epidemiologist Mauricio Barreto of the Federal University of Bahia in Salvador, Brazil.
Project after project has demonstrated that cleaner water, proper sanitation, and hygiene education can improve the health of communities. Yet few studies have measured the impact of interventions citywide, and none has focused on sanitation, says Barreto. Now, an ambitious project in Salvador that he led claims to have done just that, documenting for the first time the health benefits of expanding sewer systems.
A decade ago in Salvador, 80% of the 2.5 million residents had flush toilets in their homes. Outside of wealthy neighborhoods, however, few toilets were linked to sewers; nearly three-fourths of the residents relied on septic tanks or, more commonly, flushed waste into creeks, streets, and the like. In 1996, the city received a loan from the Inter-American Development Bank and invested about $220 million in a project that laid 2000 kilometers of sewer pipes for more than 300,000 homes. "Very few cities in the world have made an investment in sanitation on this scale in such a short time," says Barreto. "We saw it as a great opportunity to see the effects on health."
As Barreto and co-workers explained in the 10 November 2007 issue of The Lancet, they recorded cases of diarrhea in 841 children before the intervention and in 1007 other children after the pipes were laid. The children, who were no more than 3 years old and had similar living conditions in 24 sentinel areas, were followed for more than 6 months by fieldworkers who came to their homes twice a week. Citywide, diarrhea dropped 22%, and it fell 43% in neighborhoods that had the highest diarrheal prevalence before the intervention. Neither the researchers nor the city provided hygiene education, and hygiene behavior did not explain differences in diarrhea prevalence. The study team concluded that the sewage hookups primarily prevented transmission of diarrhea by reducing exposure to feces in the "public domain"--that is, in open sewers. "[The benefit] wasn't dependent on whether your house had a connection," explains co-author Sandy Cairncross, a water engineer at the London School of Hygiene and Tropical Medicine in the U.K. "It was the extent of coverage of sewers in your neighborhood to which people could connect."
Demographer Narayan Sastry of the University of Michigan, Ann Arbor, commends the researchers but questions whether the findings will apply elsewhere. He notes that other cities in Brazil have much higher connection rates to sewer systems and that it's easiest to see a dramatic impact in areas where none existed, as in some of the sentinel areas in Salvador.
Brazil's sanitation shortcomings pale, too, in comparison with many countries in sub-Saharan Africa and south Asia that lack sewage systems and clean water supplies. In these less developed countries, simpler and cheaper interventions can have a big impact, says Albert Wright, a water and sanitation engineer and consultant in Woodbridge, Virginia. "The tools are there," says Wright, a native of Ghana who has worked at the World Bank. "It's just how you apply them."
Leaders in many cities in developing countries make the mistake of wanting to replicate the sewer systems of wealthier countries, Wright contends. "They think they must have conventional sewage like New York or Los Angeles, and they try to design a centralized system," he says. But a larger system means bigger pipes and higher costs. "They look at the high cost and have a sense of hopelessness, so they put the plans on the shelf," Wright says. These cities, he says, would be better off designing neighborhood sewer systems similar to the ones recently built in Bangkok, Thailand.
In some locales that can't afford sewage systems, basic, well-designed latrines can significantly improve sanitation. Wright points to work he does with WaterAID, a nonprofit that builds dry pits and pour-flush latrines that use pairs of pits. When one pit fills, the latrine diverts to the second. After 2 years, the contents of the first pit can be removed and used as fertilizer--at which point the pit is again ready for human waste.
Although experts disagree about how to get the most bang for the buck, there's wide consensus that there aren't enough available bucks. "Diarrhea kills more children than AIDS, tuberculosis, and malaria put together," says Cairncross. "Yet there isn't a global fund for diarrhea. All politicians would like an airport or a train station named after them but not a sewage plant." Also, there's often a disconnect between local health and water agencies, he says. Further complicating matters, private enterprises frequently run water and sanitation services. And as the Salvador study highlights, scant data exist to help municipalities make tough choices.
The United Nations has declared 2008 the International Year of Sanitation, which Barreto welcomes--albeit with a measure of skepticism. "The U.N. has been very, very shy when it comes to sanitation," he says, adding that it is no longer acceptable. "Societies have to make this a priority."