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SECTION ONE
UROGENITAL TRACT INFECTIONS

INTRODUCTION TO SECTION I

We begin this text with a discussion of infections of the genitourinary tract for two reasons. First, the number of microorganisms that frequently cause infection in these organs is somewhat limited. Second, urinary tract infections (UTIs) and sexually transmitted infections (STIs) are two of the most common reasons why young adults, particularly women, consult a physician. UTIs are examples of endogenous infections, i.e., infections that arise from the patient’s own microbiota. In the case of UTIs, the microbes generally originate in the gastrointestinal tract and colonize the periurethral region before ascending the urethra to the bladder. STIs are exogenous infections; i.e., the infectious agent is acquired from a source outside the body. In the case of STIs, these agents are acquired by sexual contact.

UTIs are much more common in women than in men for a number of reasons. The urethra is shorter in women than in men, and straight rather than curved as in men, making it easier for microbes to ascend to the bladder. Prostatic secretions have antibacterial properties, which further protects the male. The periurethral epithelium in women, especially women with recurrent UTIs, is more frequently colonized with microorganisms that cause UTIs. It should also be noted that the incidence of UTIs is higher in sexually active women, as coitus can introduce organisms colonizing the periurethral region into the urethra. The incidence of nosocomial UTIs, however, is similar in women and men. In these infections, catheterization is the major predisposing factor.

The incidence of STIs is similar in both heterosexual men and women; however, the morbidity associated with these infections tends to be much greater in women. In particular, irreversible damage to reproductive organs, caused by both Chlamydia trachomatis and Neisseria gonorrhoeae, is all too common. Infections with these two organisms are almost always symptomatic in males, though the few men who do not have symptoms can be responsible for infecting many partners. By contrast, a significant number of women may be infected asymptomatically at first. They may manifest signs and symptoms of infection only when they develop pelvic inflammatory disease, which can result in sterility. Fetal loss or severe perinatal infection may be caused by two other STI agents, herpes simplex virus and Treponema pallidum, the etiologic agent of syphilis.

Important agents of genitourinary tract infections are listed in Table 1. Only organisms in this table should be considered in your differential diagnosis for the cases in this section. You should note that not all organisms that can be spread sexually, such as hepatitis B virus and Entamoeba histolytica, are listed. This is because these infections do not have genitourinary tract manifestations.

TABLE I SELECTED GENITOURINARY TRACT PATHOGENS

ORGANISM	GENERAL CHARACTERISTICS	SOURCE OF INFECTION	DISEASE MANIFESTATION
Bacteria
Actinomyces spp.	Anaerobic, Gram-positive bacilli	Endogenous	PIDa associated with intrauterine device usage
Aerococcus spp.	Catalase-negative, Gram-positive cocci	Endogenous	Community- or health care-associated UTIb
Bacteroides fragilis	Anaerobic, Gram-negative bacillus	Endogenous	Pelvic abscess
Chlamydia trachomatis	Obligate intracellular pathogen (does not Gram stain)	Direct sexual contact	Urethritis, cervicitis, PID
Enterobacter spp.	Lactose-fermenting, Gram-negative bacilli	Endogenous	Community- or health care-associated UTI
Enterococcus spp.	Catalase-negative, Gram-positive cocci	Endogenous	Health care-associated UTI
Escherichia coli	Lactose-fermenting, Gram-negative bacillus	Endogenous	Community- or health care-associated UTI
Haemophilus ducreyi	Fastidious, pleiomorphic, Gram-negative bacillus	Direct sexual contact	Chancroid (painful genital ulcer)
Klebsiella pneumoniae	Lactose-fermenting, Gram-negative bacillus	Endogenous	Community- or health care-associated UTI
Morganella morganii	Lactose-nonfermenting, Gram-negative bacillus	Endogenous	Community- or health care-associated UTI
Mycoplasma hominis	Lacks a cell wall (does not Gram stain)	Endogenous; direct sexual contact	Pyelonephritis, PID
Neisseria gonorrhoeae	Gram-negative, intracellular diplococcus	Direct sexual contact	Urethritis, cervicitis, PID
Proteus mirabilis	Lactose-nonfermenting, swarming, Gram-negative bacillus	Endogenous	Community- or health care-associated UTI
Pseudomonas aeruginosa	Lactose-nonfermenting, Gram-negative bacillus	Catheterization	Health care-associated UTI
Staphylococcus saprophyticus	Catalase-positive, Gram-positive coccus	Endogenous	Community-associated UTI
Treponema pallidum	Spirochete (does not Gram stain)	Direct sexual contact; vertical, mother to child	Chancre (painless genital ulcer); primary, secondary, tertiary syphilis; neonatal syphilis
Ureaplasma urealyticum	Lacks a cell wall (does not Gram stain)	Endogenous; direct sexual contact	Urethritis, urethroprostatitis, epididymitis, chorioamnionitis
Fungi
Candida spp.	Yeasts with pseudohyphae	Endogenous	Vaginitis, health care-associated UTI, balanitis
Parasites
Phthirus pubis	Crab lice	Direct sexual contact	Pubic hair infestation
Trichomonas vaginalis	Protozoan	Direct sexual contact	Vaginitis
Viruses
Adenoviruses	Nonenveloped DNA viruses	Exogenous exposure	Hemorrhagic cystitis
Herpes simplex viruses (HSV-1 and -2)	Enveloped DNA viruses	Direct sexual contact; vertical, mother to child	Recurrent genital ulcers, fetal/neonatal infections, encephalitis
Human immunodeficiency viruses (HIV-1 and -2)	Retroviruses	Direct sexual contact; blood and body fluids; vertical, mother to child	AIDS, neonatal infection, dementia
Human papillomavirus	Nonenveloped DNA virus	Direct sexual contact	Genital warts, cervical and anal carcinoma

^a PID, pelvic inflammatory disease.

^b UTI, urinary tract infection.