Bacterial infections

Alessio Fasano

Enteric infections exact a heavy toll on human populations, particularly among children. Despite the explosion of knowledge on the pathogenesis of enteric diseases experienced during the past decade, the number of diarrheal episodes and childhood deaths reported worldwide remains of apocalyptic dimensions. In the next 15 s, a child somewhere in the world will die from diarrhea. Worldwide, it is estimated that 6-60 billion cases of gastrointestinal illness occur annually, the vast majority being severe enough and affecting so many unprivileged populations to pose a serious global health burden. In overpopulated developing countries, poor sanitation and hygiene, unsafe water supplies and limited education contribute to the propagation of diarrheal diseases. In industrialized nations, diarrhea had been thought of as more of an inconvenience rather than a serious cause of illness, but recent attention to food contamination by pathogens such as Salmonella and Escherichia coli, in combination with a growing population of immunosuppressed patients, has led to increased recognition of their impact. The situation is further complicated by the recent escalation of international terrorism that is raising the risk of epidemics of enteric pathogens beyond the boundaries of natural endemic areas.

The appreciation of these multifaceted aspects of the problem is pivotal for full comprehension of the threat that diarrheal diseases pose to public health and for appropriate allocation of resources and efforts to tackle them. However, there are a series of obstacles that have historically hampered this process, including non-standardized definitions of disease and symptoms; failure to identify a causative agent in many, if not most, cases of disease; failure to report episodes to health authorities; and the existence of incompatible reporting systems. Most of all, the lack of long-term commit ment of rich countries to finance sanitation campaigns to treat and prevent diarrheal diseases in endemic areas has been a key limiting factor in tackling the burden of gastrointestinal diseases. Nevertheless, bacterial genome sequencing and better understanding of the pathogenic mechanisms involved in the onset of diarrhea, particularly concerning the elaboration of toxin (Figure 10.1), are finally leading to preventive interventions, such as enteric vaccines, that may have a significant impact on the magnitude of this human plague.

The majority of acute infectious diarrheal illnesses in both children and adults in developing countries are due to bacteria (Table 10.1). The risk factors for transmission of these pathogens are higher in these countries, owing to increased exposure to the organisms (by contact with feces, water, food and fomites) and increased susceptibility of the host due to malnutrition.

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