Public health leaders appear to have a very high confidence-to-knowledge ratio regarding Ebola in the U.S. They act like Ebola will behave the same way here as it has in Africa, where the endemic diseases are different and the immunity of the population is different.

Disease dynamics are different in each population infected. Two Dallas health care workers have been infected despite precautions that should have worked based on experience from Africa. This is just the tip of the public health problem.

Let me introduce the basic reproductive ratio, which is the number of uninfected people that one infected person is expected to transmit the disease to. A recent study estimated the basic reproductive ratio of Ebola in West Africa – a part of the world with very limited resources, poor hygiene and a strapped health care system – to be about 1-to-2.

Compare this with the U.S. where, despite many more resources, one symptomatic person in Dallas passed the disease on to at least two uninfected people while he was in isolation. What, then, would be the basic reproductive ratio of Ebola on the streets of America, where most of us don’t walk around wearing gown, gloves and mask? Who is to say it won’t be 1-to-5 or higher (think smallpox)?

If one symptomatic person causes new infections over a week’s time, then a basic reproductive ratio of 1-to-2 could mean an initial infection spreading to over 4,000 people in 12 weeks. A basic reproductive ratio of 1-to-5 might cause the infection of over 244 million in this same time frame. (Take these numbers with a grain of salt.)

Time for panic? No, but it’s not a time for confidence, either. It’s time to recognize that Ebola in this country may play by different rules, and nobody yet knows what those rules are.

Paul Gerrard

Portland

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