Friday, September 02, 2005

Katrina: out now

During the anthrax episode, the Secretary of Health and Human Services Tommy Thompson repeatedly provided incorrect information to the news media on the number of spores required to produce an infection. The same misinformation was often repeated by public health authorities. Failure to communicate the fact that the risks from even a small number of spores could result in infection may have contributed to the deaths of two postal employees at the Brentwood facility in Washington, DC.

Misinformation from those who should know better is also occurring in the aftermath of hurricane Katrina. DHHS Secretary Leavitt, for example, has warned of the risk of "typhoid and cholera" as a result of contaminated water, while others have talked generally of mosquito-borne disease and the hazards caused by dead people and animals. It is time to separate the real risks from the phantom risks.

Diarrheal disease from contaminated water is a concern, but not cholera and probably not typhoid. In order to get these diseases the water has to be contaminated with the organisms that cause those diseases, neither of which is endemic in that region. What is more likely is gastroenteritis or hepatitis A from enteric viruses or bacteria. Most are spread by the fecal-oral route, which means they are not spread directly person to person. If they get in a contaminated, piped water supply they can cause an epidemic, because piped water is an efficient way to distribute pathogens to a population. But localized contamination of flood waters is not. Individuals can get serious diarrheal disease and even die of consequent dehydration, but there is not likely to be a point source epidemic of cholera or typhoid or even diarrheal disease, only sporadic cases (which may be relatively numerous but not epidemic in nature). Lack of clean water and food can produce a risk of diarrhea and dehydration and must be attended to quickly, but not to prevent an epidemic.

Similarly the presence of dead animals and people is not a health hazard. Dead animals decompose naturally in the environment. Unless they were infected with a contagious organism before death, they will not themselves become the source of disease. The persisten concern in mass disasters over unburied bodies is an urban myth. Mass disasters like floods rarely cause epidemic disease and to suggest otherwise results in misplaced concern and potential diversion of resources from more important issues.

Mosquito-borne illness is a potential concern for some, but needs to be properly understood. Being bitten by mosquitoes is not a health hazard. The mosquitoes themselves must be vectors for a pathogenic agent like malaria or West Nile. Almost all malaria cases in the US are in people exposed and infected elsewhere who travel to this country and become sick shortly after arriving. We do not have endemic malaria, at least not at this point (global warming might change that, of course). West Nile is a possibility, because there are an unknown number of infected birds and possibly other animals in that region. However the mosquitoes that multiply in the wake of the flooding have to be the kind that both bite infected birds and bite humans. We don't know what the disaster did to the ecological niches of the potentially infected animal population nor do we know whether any increase in s specific mosquito population will be in the kind of "bridge vector" capable of biting both humans and whatever existing infected animals are around. So even a huge increase in the mosquito population does not necessarily, or even probably, mean an outbreak of West Nile or other mosquito-borne illnesses. This is important because the fear of "an epidemic" might encourage interventions that themselves carry undue risk, such as broadcast spraying of pesticides to kill adult mosquitoes. Mosquitoes reproduce exponential quickly and these techniques have not been shown to interrupt the transmission of human disease. They have the potential to just add one more biologically active toxin to the environment.

The biggest health hazards may well be those we would classify under "injury." Heat-related illness might be at the top of the list here. As body core temperatures rise above 105 degrees F., mortality increases quickly. The high heat and humidity of the area, coupled with dehydration are a significant health hazard that requires intervention by providing fluids and cooler shelters. The many sources of physical injury, whether from feral animals (snakes, alligators, etc.), sharp metal debris, falls and injuries in an environment where the hazards are numerous and not easily visible can result in substantial accumulated morbidity and even mortality. The only remedy is removal of people to a safer environment, which should be the top priority. this is also true for the many chronically ill and vulnerable people who require medication, external support from power dependent devices and supervision.

The situation is complex but the bottom line here is simple: mobilize resources to remove people from the area as quickly as possible, while providing fresh food and water to those waiting evacuation. This is something a well-organized military force, like the National Guard, should have been equipped to do from the outset. If they can plan how to put hundreds of thousands of soldiers to invade an area in a twelve hour period, they can also plan how to remove civilians in a three day period.

Or can they?