Emerging infectious diseases 1997-1998: the role of molecular epidemiology.

In the last year, the global public health com-munity has continued to be confronted and chal-lenged by emerging infectious diseases. As evi-dent from studying a list of emerging diseases, al-most every year at least one new human pathogenis recognized or the microbial cause of a previ-ously identified disease is determined. The lastyear has proven to be no exception, with the firsthuman illnesses due to an avian strain of influenza[influenza A (H5N1)] recognized in the latter halfof 1997 in Hong Kong (K Subbarao et al. 1998Science 351: 393-396, KY Yuen et al. 1998 Lan-cet 351: 467-471). Other firsts during 1997-1998were the initial reports of nosocomial infectionscaused by strains of Staphylococcus aureus withreduced susceptibility to glycopeptides (i.e. van-comycin) from Japan (K Hiramatsu et al. 1997Lancet 350: 1670-1673) and the United States(CDC 1997a MMWR 46: 813-815) and an out-break of hantavirus pulmonary syndrome identi-fied in Chile (CDC 1997b MMWR 46: 949-951).Other prominent emerging infections contin-ued to garner attention. In the United States, a clus-ter of Escherichia coli O157:H7 cases generated amassive recall of ground beef (CDC 1997c MMWR46 : 777-778), and for the second year in a rowwidespread outbreaks of cyclosporiasis linked toimported fresh raspberries, and other producesources, were recognized (CDC 1997d MMWR 46 :461-462).Reemergence of infectious diseases thought tobe under control also occurred in the last year.Large outbreaks of measles were identified in SaoPaulo and Rio de Janeiro, Brazil, representing thefirst significant outbreaks of measles in SouthAmerica in several years (WHO 1997 WeekEpidemiol Rec 72: 349-353). Dengue fever con-tinued to spread to many urban centers of theAmericas and Asia (PAHO 1997 Epidemiol Bull18: 1-6, AL Richards et al. 1997 Am J Trop MedHyg 57: 49-55, G Kouri et al. 1998 Emerg InfectDis 4: 89-92). In Africa, a large outbreak of RiftValley fever occurred in Somalia and Kenya (CDC1998 MMWR 47: 261-264). In the United States,a multistate outbreak of hepatitis A linked to fro-zen imported strawberries was reported (CDC1997e MMWR 46: 288, 295).Despite the many newly recognized pathogensand the increasing complexity of infectious dis-eases, in most parts of the world the infrastructureto control and prevent these diseases has erodedover the last 20 years (Ciset 1995 Report of theNSTC Ciset Working Group on emerging and re-emerging infectious disease). However, now in-creasing attention is being given to the problem ofemerging infectious diseases, culminating inemerging infectious diseases being chosen as thetheme for 1997’s World Health Day (AAWH 1997Resource Booklet for World Health Day). Slowlythis increased attention is beginning to translateinto long overdue improvements in global surveil-lance and response capacity (JW LeDuc 1996JAMA 275: 3318-3320).Enhanced capacity is crucial, since the under-lying causes of disease emergence show no signsof abatement. These factors include global popu-lation growth and demographic change; humanbehaviors which promote microbial proliferation;technologic innovation with unintended conse-quences; changes in land use patterns and the en-vironment; global commerce and population move-ment; microbial adaptability; and failure to effec-tively utilize public health and clinical tools (SSMorse 1995 Emerge Infec Dis 1: 7-15). In gen-eral, it is the interplay of these factors rather thanany single one which results in most emerging in-fections.To successfully address emerging infectiousdiseases, public health must develop and harnessnew tools. Examples include computerization andelectronic transmission of surveillance data, newand rapid diagnostic laboratory assays, and utili-zation of satellite-based global positioning systems.One of the most powerful tools which has devel-oped in recent years is the field of molecular epi-demiology. This growing discipline has revolu-tionized our understanding of disease transmission