Sexually Transmitted Diseases

The world continues to live with the ironic realization that the most intimate form of human relations, that of sexual interactions, carries the threat of serious disease. Sexually transmitted diseases (STDs), once known as venereal diseases, have menaced humankind since the dawn of recorded history. There are references to STDs in Egyptian papyri dating to 1550 BCE, and according to biblical scholars, there are similar references in the Old Testament (Holmes et al. 1999). STDs operate at the intersection of individual human behaviors, collective sociodemographic trends, and specific disease pathogens. They are diseases caused by bacteria, viruses, protozoa, fungi, and ectoparasites. In society and within the lives of families and individuals, STDs continue to inflict considerable suffering, trauma, serious medical conditions, and medical expense. They can often stigmatize the infectee; they also can cause death. Despite powerful treatments including newer antibiotics, better diagnostic tools using advanced technologies, extensive prevention programs, and increased international awareness, STDs remain among the most common reported diseases.

Tragically, they have a global reach that in many countries dwarfs the burden in the United States. The World Health Organization estimated that in 1999, among women and men aged fifteen to forty-nine years, there were approximately 340 million new cases of the most common, nonviral, sexually transmitted diseases that occurred throughout the world. They were syphilis (12 million), gonorrhea (62 million), chlamydia (92 million), and trichomoniasis (174 million). STDs most commonly affect people when they are between the ages of fifteen and forty-four, during their peak years of economic production (Ober and Piot 1993). This is of particular concern to developing countries.

For these four STDs and several others (there are more than twenty-five pathogens that can be transmitted by sexual intercourse), their spread in a population is a function of the average number of new cases caused by an infected person (often referred to as the force of infectivity). This number is the product of the efficiency of transmission of the STD, the average duration of infectiousness of the STD, and the mean number of different sexual partners per unit time (Anderson and May 1991). The use of numerical methods using this kind of methodology has allowed population- and country-specific estimates for incidence and prevalence of the most common STDs.

The three most common and threatening sequelae (i.e., after-effects) of STDs to infected individuals are impaired fertility for women, adverse pregnancy outcomes, and increased susceptibility to the human immunodeficiency virus (HIV), the virus that causes acquired immunodeficiency syndrome (AIDS). STDs cause acute illnesses, long-term suffering and disability, and infertility. Related psychological and medical consequences have an enormous global economic impact.

Since World War II, advances in epidemiology, disease surveillance, behavioral and social sciences, demographics, and medical science have greatly contributed to a better understanding of how STDs occur, are sustained, and shift into new populations in society; how they interact with each other; how several STDs can be successfully treated and cured (although many still cannot); and, importantly, how they and their most common sequelae can often be prevented. Despite these modern advances, STDs continue to imperil society, families and other loved ones, and individuals.

Although difficult to estimate (approximately 12 million infections from STDs occur annually in the United States), two-thirds of the infections from STDs occur among people less than twenty-five years of age (Noegel et al. 1993). Women and the poor suffer disproportionately, and it is estimated that one of every four people in the United States will have an STD in his or her lifetime. STDs are most commonly transmitted either from males to their female sex partners or from females to their male sex partners. Male to male transmission occurs often with some STDs, whereas female to female transmission occurs infrequently with nearly all STDs. Of the more than twenty-five known pathogens that are classified as causing STDs in humans, only the most important will be addressed here.