Over the past few months, yet another epidemic has come to trouble our unhappy world. Shortly after SARS was identified, the entire globe was put on notice. Although the new illness is not as deadly as many other infectious diseases (compare the 500 or so confirmed dead of SARS with the 8,500 who die each day of AIDS), it has sent ripples throughout the world economy. It’s perhaps easier to notice from my HIV clinic in Haiti that SARS was so quickly seen as a crisis because it affects areas of high economic traffic, whereas AIDS and tuberculosis mostly affect populations deemed irrelevant to the global economy.

In 1946 the new constitution of the World Health Organization (WHO) warned that “unequal development in different countries in the promotion of health and control of disease, especially communicable disease, is a common danger.” The world is now even more divided between medical haves and have-nots, and infectious pathogens still exploit these social inequalities. They are why we have not eradicated polio, measles or malaria; why AIDS is disappearing among American children even as it claims the lives of more and more children in Africa and Asia.

Inequity has already shaped SARS. The disease emerged at the border between a low-income area with rapidly privatizing health services (China) and a high-income area with good public health (Hong Kong). Weak surveillance systems–a symptom of declining public health infrastructures–make it impossible to know when SARS first emerged or how big a problem it is. Many sick with SARS were saved by intensive care delivered in excellent hospitals, while SARS patients without access to such care faced worse outcomes.

Some lessons may be drawn from SARS, even at this early stage. First, there is the question of resources. Our shock at SARS images–commuters in Asia wearing masks, empty airplanes and marketplaces–speaks volumes, for in parts of the world where tuberculosis, AIDS and malaria reap their grim harvest of 6 million lives a year (almost all preventable deaths) there are few if any trains, airplanes or masks, and markets have long been miserable. A colleague in China writes to say his own work on tuberculosis, a disease of far greater significance there, may be halted because “staff at all levels are moving toward the control and battle on SARS.” Our zero-sum approach to infectious-disease control means that resources are drawn away from big killers that do not rock international markets or inconvenience tourist itineraries.

A second lesson: We permit the erosion of public health infrastructures at our peril. Across the globe, healthcare privatization is advanced by international agencies and governments far more powerful than the WHO. These changes, sometimes called “healthcare reform,” usually involve cutbacks in healthcare for the poor and in the surveillance systems necessary to respond to new health threats. As China privatizes, it is seeing the erosion of its public health infrastructure, a trend that has already reached its nadir in much of Africa, where the situation is worse now than it was under colonial rule. Public health infrastructures must be preserved and rebuilt.

Third, disease surveillance and control must be as transnational as the epidemics themselves–not unilateral or bilateral. As SARS broke out, public-health specialists found themselves shouted down by mayors or ministers of trade and tourism, not only in authoritarian China but even in Canada. The WHO correctly and courageously issued travel advisories, despite being derided for triggering panic, fueling prejudices and damaging the global economy. The job of the WHO is to protect health rather than tourism or stock markets; thankfully, the international body proved itself able to resist national interests in its response.

Fourth, to encourage international agencies to issue advisories and declare emergencies, we must assure that resources, not rebukes, follow. Declaring an epidemic an emergency has often failed to produce rapid cash. The WHO declared tuberculosis and AIDS international emergencies more than a decade ago, but it took ten years and unremitting activism to develop novel funding mechanisms like the Global Fund to Fight AIDS, Tuberculosis and Malaria. Creating such a fund was a major victory in the struggle for multilateral responses to health emergencies, yet the fund languishes as wealthy donor nations fail to contribute their part.

SARS reminds us that debates over unilateralism versus multilateralism, raised around Iraq, must be extended to international health. Adequate responses to the great plagues of our times–a dubious honor SARS has yet to earn–will not come from a coalition of the unwilling. If wealthy nations let the Global Fund and other multilateral efforts die on the vine, then one thing is sure: There will be a less coordinated response to the next SARS.

AIDS has already taught us about how quickly a new pathogen can spread across the world. SARS is another warning about the intimacy of our connections, even across deep divides of language, culture and class. William Budd, a doctor from Victorian England, writing of typhoid fever in 1874, put it this way: “The disease not seldom attacks the rich, but it thrives most among the poor. But by reason of our common humanity we are all, whether rich or poor, more nearly related here than we are apt to think. The members of the great human family are, in fact, bound together by a thousand secret ties, of whose existence the world in general little dreams. And he that was never yet connected with his poorer neighbour, by deeds of charity or love, may one day find, when it is too late, that he is connected with him by a bond which may bring them both, at once, to a common grave.”