Chapter 2: Threats to public health security.

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Chapter 2 explores a range of threats to global public health security, as defined by the international health regulations (2005), which result from human actions or causes, from human interaction with the environment, and from sudden chemical and radioactive events, including industrial accidents and natural phenomena. It begins by illustrating how inadequate investment in public health, resulting from a false sense of security in the absence of infectious disease outbreaks, has led to reduced vigilance and a relaxing of adherence to effective prevention programmes.

The new regulations are no longer limited to the scope of their original six diseases--cholera, plague, relapsing fever, smallpox, typhus and yellow fever. Rather, they address "illness or medical conditions, irrespective of origin or source that present or could present significant harm to humans" (1).

Such threats to public health security, be they epidemics of infectious diseases, natural disasters, chemical emergencies or certain other acute health events, can be traced to one or more causes. The causes may be natural, environmental, industrial, accidental or deliberate but--more often than not--they are related to human behaviour.

This chapter explores the threats to global public health security, as defined by IHR (2005), which can result from human action or inaction and natural events. The importance of the more fundamental causes of health security embedded in the social and political environments that foster inequities within and between groups of people will be discussed in subsequent publications.

HUMAN CAUSES OF PUBLIC HEALTH INSECURITY

Human behaviour that determines public health security includes decisions and actions taken by individuals at all levels--for example, political leaders, policy-makers, military commanders, public health specialists and the general population--which have dramatic health consequences, both negative and positive. The following examples illustrate the public health security repercussions when human behaviour is influenced by situations of conflict and displacement or attitudes of complacency, lack of commitment, and mistrust and misinformation.

Inadequate investment

Inadequate investment in public health, resulting from a false sense of security in the absence of infectious disease outbreaks, can lead to reduced vigilance and a relaxing of adherence to effective prevention programmes. For example, following the widespread use of insecticides in large-scale, systematic control programmes, by the late 1960s most of the important vector-borne diseases were no longer considered major public health problems outside of sub-Saharan Africa. Control programmes then lapsed as resources dwindled, and the training and employment of specialists declined. The result was that within the next 20 years, many important vector-borne diseases including African trypanosomiasis, dengue and dengue haemorrhagic fever, and malaria emerged in new areas or re-emerged in areas previously affected. Urbanization and increasing international trade and travel have contributed to rapid spread of dengue viruses and their vectors. Dengue caused an unprecedented pandemic in 1998, with 1.2 million cases reported to WHO from 56 countries. Since then, dengue epidemics have continued, affecting millions of people from Latin America to South-East Asia. Globally, the average annual number of cases reported to WHO has nearly doubled in each of the last four decades.

Inadequate surveillance results from a lack of commitment to build effective health systems capable of monitoring a country's health status. This is illustrated by the rapid global emergence and spread of HIV/AIDS in the 1970s. The presence of a new health threat was not detected by what were invariably weak health systems in many developing countries, and only belatedly became a matter of international concern when it manifested itself in the first cases in the United States. Figure 2.1 shows developments over 25 years dating from this event at the beginning of the 1980s.

Surveillance is the cornerstone of public health security. Without appropriately designed and functioning surveillance systems, unusual but identifiable health events cannot be detected, monitored for their likely impact, quantified over time or measured for the effectiveness of interventions put in place to counteract them (see Figure 2.2).

The inability of surveillance systems to recognize new disease trends is not confined to poorer countries. For instance, the first cases of AIDS were detected and characterized in the United States not by surveillance but by serendipity. Epidemiologists at the United States Centers for Disease Control and Prevention (CDC) observed an unusual number of requests to their orphan drug repository for antimicrobials to treat pneumonia caused by Pneumocystis carinii, a rare parasitic infection but one that is common in AIDS cases (2). Yet, what soon became known as AIDS had been occurring for perhaps many years in Africa and Haiti--poorly detected and poorly characterized. Inadequate surveillance systems, universal in low and middle income countries, are not capable of recognizing unusual health events. Similarly, because these systems are poorly funded and diagnostic facilities are limited, the systems do not allow for the identification and monitoring of any but a few specific illnesses, for example, tuberculous. Ministries of health are doubly compromised because, without better surveillance, it is difficult for them to mount interventions or measure their effectiveness.

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In addition to limited disease surveillance capacity and data, early efforts to control the AIDS epidemic were also hampered by a lack of solid data on sexual behaviour, whether in Africa, Haiti, or the United States and other industrialized countries. In the industrialized world, the 1960s was a period of scientific advances and rapid social change. The widespread availability of oral contraception contributed to the apparent liberalization of sexual mores that was furthered by the profound social changes of that period. Coupled with these developments, attitudes towards and among homosexually active men became more liberal, particularly in the big cities of the United States, with a marked migration of gay men to certain key cities. Despite these significant social and attitudinal changes, no scientific study of sexual behaviour, and its relationship to the emergence of sexually transmitted diseases, had been carried out in the United States since the 1950s, and these were long out of date by the time AIDS appeared as a major public health threat.

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As inadequate as behavioural data were in the industrialized world, they were practically non-existent in the developing world. The understanding of HIV/AIDS in the context of sexuality in the developing world took years to develop and is still poorly understood. Only in recent years, a quarter of a century after the description of AIDS, have population-based surveys of sexual behaviour (demographic and health surveys) been conducted that allow a better understanding--supported by valid scientific evidence--of sexual behaviour in countries on multiple continents heavily affected by HIV/AIDS (3).

Unexpected policy changes

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Even with reliable operations in place, unexpected policy changes in public health systems can have lethal and costly repercussions. Such was the case in August 2003, when unsubstantiated claims originating in northern Nigeria that the oral polio vaccine (OPV) was unsafe and could sterilize young children led to governments ordering the suspension of polio immunization in two northern states and substantial reductions in polio immunization coverage in a number of others. The result was a large outbreak of poliomyelitis across northern Nigeria and the reinfection of previously polio-free areas in the south of the …