Chapter 9. Proctitis & Proctocolitis

Essentials of Diagnosis

• • A thorough sexual history, including information about the practice of rectal sex (receptive or insertive) or oral-anal sex, with or without condoms.
• • Screening for rectal pathogens based on sexual risk history.
• • Anoscopy in patients with symptoms of anorectal pain, tenesmus, or discharge.
• • Collection of specimens for gonorrhea, chlamydia, and serologic tests for syphilis and HIV, and stool specimens for culture and ova and parasite examinations in patients with symptoms of proctocolitis.

General Considerations

Proctitis is an inflammatory condition of the rectum that usually occurs secondary to infection introduced during sexual activity. A more extensive condition—proctocolitis—may occur after oral ingestion of a pathogen that produces colorectal inflammation. Both conditions are noted more frequently in men who have sex with men (MSM). Proctitis is commonly caused by gonorrhea, chlamydia, and herpes simplex virus (HSV) infections, and proctocolitis by enteric bacteria or parasites.

The incidence of acute, sexually transmitted proctitis and proctocolitis, which decreased dramatically during the 1980s and early 1990s, began increasing again in the mid-1990s. As a consequence of successful antiretroviral therapy for HIV infection and AIDS, declining concern about HIV and AIDS, and renewed physical health, many HIV-infected men in the United States have increasingly been engaging in sexual risk behaviors associated with the spread of STDs. Consistent condom use between HIV-infected sex partners in some cities has also declined, resulting in substantial increases in rates of syphilis and rectal STDs.

Pathogenesis

Sexually transmitted intestinal infections may be transmitted by direct rectal inoculation or indirectly in the course of oral-anal contact. Conventional sexually transmitted diseases (STDs) most often cause rectal infections through direct inoculation by anal intercourse, although perineal contamination by cervicovaginal secretions among women has been described. Chlamydia trachomatis and Neisseria gonorrhoeae infect columnar epithelium and infect the anorectal mucosa via oral-genital and rectal insertive intercourse. HSV, human papillomavirus, and Treponema pallidum infect stratified squamous epithelium and can be transmitted similarly to the anorectal region. Although not considered “classical” STDs, enteric pathogens, parasites, and hepatitis A and B can be transmitted during direct oral-anal contact, (anilingus) or during oral-genital contact after rectal intercourse. Exposure to as few as 10–100 organisms of Shigella, Entamoeba histolytica cysts, or Giardia lamblia cysts may precipitate infection.

Risk Factors

Multiple partners, anonymous partners, and individual sexual practices that increase the risk of acquiring specific diseases are associated with increased risk of acquiring any STD. Individuals who engage in receptive anal intercourse or anilingus are at high risk for acquiring sexually transmitted proctitis and enteritis.

Anal intercourse continues as a prevalent sexual practice in both homosexual and heterosexual populations. Studies report that up to 43% of adult women have participated in anal intercourse. Teen definitions of sexual activity may not include oral or anal sex, and the prevalence of anal sex among teens engaging in abstinence-only programs is unknown. Clinicians, social workers, and disease intervention specialists must develop a tactful approach for eliciting information regarding anorectal sexual exposure and other high-risk behaviors, because this information may result in more rapid disease detection, treatment, and control.

Prevention

Because the incidence of acute sexually transmitted rectal and gastrointestinal syndromes is increasing, the diligence of clinicians in counseling patients regarding safer sex practices should not lessen. All patients, regardless of their sexual preferences, should have a careful history to elicit information about gender of sex partners, specific sexual practices, and the method and frequency of condom or other barrier use. This will provide important clues to direct proper evaluation, specimen collection, therapeutic choices, and counseling regardless of patients’ presenting symptoms. Consistent condom use and handwashing using soap and water have been recommended to reduce the transmission of gastrointestinal infections. Although latex barriers are also recommended during oral-anal sex, few persons in practice use that barrier method. Vaccination against hepatitis A is an effective preventive measure, particularly in persons who engage in anal or oral-anal sex. Sexually active persons should be informed about these measures, evaluated to determine the need for hepatitis A vaccination, and offered vaccination, if deemed susceptible.

Clinical Findings

Several pathogens are associated with sexually transmitted intestinal syndromes (see Table 9–1). Symptoms and clinical manifestations vary, depending on the pathogen involved and the location of the infection. The latter half of this chapter discusses symptoms and signs, laboratory findings, and treatment for common pathogens that can cause proctitis and proctocolitis.

Polymicrobial infection often occurs and can cause upper intestinal and perianal symptoms. Nonetheless, asymptomatic infections are prevalent, and the clinician should routinely inquire about rectal exposure regardless of the patient’s sexual preferences, so as to perform screening tests or anoscopic evaluation when appropriate.

Proctitis

Inflammation involving the rectal mucosa is termed proctitis. The perianal area up to the anal verge is composed of keratinized, stratified squamous dermal epithelium. Lesions caused by syphilis, HSV, or condylomata acuminata, therefore, generally have the same appearance as they do in other genital areas. The stratified squamous epithelium gradually changes to stratified cuboidal epithelium from the anal verge up to the anorectal (pectinate or dentate) line. Infection in this area with an extensive network of sensory nerve endings may be painful, sometimes resulting in constipation or tenesmus as a result of anal sphincter muscle spasm. Above the anorectal line, the rectum is lined by columnar epithelium, and infections of this region that spare the anus are relatively painless. Anorectal sexually transmitted infections, therefore, may be asymptomatic. Symptoms of proctitis, however, include anorectal pain, mucopurulent or bloody rectal discharge, tenesmus, and constipation.

Proctocolitis

Infections that involve the rectum and the colon are termed proctocolitis. Symptoms may include those of proctitis as well as abdominal pain, bloating, cramping, and sometimes diarrhea and fever.

Initial Examination

In order to classify patients into syndromes to direct diagnostic and therapeutic choices, a thorough physical examination is essential. Careful inspection of the perianal region may detect lesions or masses that can be tested for pathogens such as HSV or sampled for darkfield examination. Anoscopy may reveal rectal exudates or rectal bleeding. If the patient has proctitis, sigmoidoscopy often reveals disease limited to the rectum, whereas with proctocolitis, the disease process extends above 15 cm, into the sigmoid colon.

Differential Diagnosis

The differential diagnosis of infectious proctitis includes gonorrhea, chlamydia (including lymphogranuloma venereum subtypes), HSV, and, rarely, syphilis. Further discussion of each of these infectious causes is provided later in this chapter. Noninfectious causes include inflammatory bowel disease and neoplastic disease (anorectal cancer). Infectious proctocolitis may be caused by extension of proctitis or other enteric bacterial pathogens (eg, Shigella or Salmonella species) or by parasites such as Entamoeba and Giardia lamblia. Other potential bacterial causes of proctocolitis, such as Campylobacter, Yersinia, and the various E coli species, are beyond the scope of this chapter.

Complications

Although most infectious causes of sexually transmitted intestinal syndromes respond readily to treatment, untreated proctitis or proctocolitis may persist and lead to abscesses, fistulae, and strictures. In the preantibiotic era, chronic infection sometimes led to rectal strictures and rectal obstruction that required surgical intervention. Rectal infections substantially increase the risk of HIV acquisition, because the inflamed rectal mucosa is rich with immunologic target cells and defects in the epithelial barrier provide an opening for viral entry.

When to Refer to a Specialist

If the diagnosis is uncertain or treatment fails to resolve the patient’s symptoms, further evaluation, including sigmoidoscopy or colonoscopy and biopsy, may be required. Radiologic imaging (eg, radiographs, computed tomography scan, and magnetic resonance imaging) has a limited role in the management of proctitis and proctocolitis, except to rule out toxic megacolon, which is usually associated with Clostridium difficile colitis.

Prognosis

The Centers for Disease Control and Prevention (CDC) classifies rectal gonococcal and chlamydial infections as “uncomplicated,” recommending the same single-dose therapy for rectal infections as for urogenital infections. Rectal infections respond similarly to uncomplicated infections at other anatomic sites, and treatment failure or persistent infection is uncommon (<5% of patients). Some experts recommend that patients with rectal gonorrhea or chlamydia undergo repeat testing at 3 months to rule out reinfection. Rectal herpes infection can be managed episodically with antiviral treatment at the earliest onset of symptoms or with chronic antiviral suppression to reduce the frequency of outbreaks.

Neisseria Gonorrhoeae

The rectum is a common site for gonococcal infection. In a recent retrospective review of 101 patients who presented to an STD clinic for evaluation of proctitis symptoms, 30% had gonorrhea. Rectal gonorrhea among MSM results from direct inoculation through receptive rectal intercourse. The rectal mucosa may also be infected in 35–50% of women with gonococcal cervicitis and in several studies carried out in the pre-AIDS era was the only site of infection in approximately 5% of women with gonorrhea. Although rectal gonorrhea in women is associated with direct inoculation through rectal intercourse, infections in women may occur without acknowledged rectal sexual contact, are positively correlated with the duration of endocervical infection, and are assumed to result from perineal contamination with infected cervical secretions.

Clinical Findings

Symptoms and Signs

Many rectal gonococcal infections are asymptomatic. A recent evaluation of rectal, urethral, and pharyngeal chlamydial and gonococcal infections among MSM attending a municipal STD clinic and a gay men’s community health center in San Francisco found a 7% prevalence of rectal gonorrhea, 84% of which was asymptomatic. When present, however, symptoms associated with gonococcal infections may be subtle and missed if not sought. Rectal gonorrhea symptoms may develop 5–7 days after exposure and include mild anorectal pain, scant bleeding, pruritus, and mucopurulent discharge manifested only by a coating of stools with exudate. Occasionally, more severe symptoms may occur; these include tenesmus and constipation. External inspection of the perirectal area and anus may rarely show erythema and discharge. Anoscopic evaluation commonly reveals mucopus in the anal canal, especially around the anal crypts. The rectal mucosa may appear completely normal or erythematous and friable, especially near the anorectal junction.

Laboratory Findings

If available, Gram stain of a rectal specimen can be performed as an immediate diagnostic tool. The sensitivity of a “blind” anorectal swab evaluated by Gram stain has been reported in the range of 40–60% compared with culture, although when positive this result is highly specific. In men with symptomatic rectal gonorrhea, Gram stain sensitivity was 79% when obtained via anoscopy compared with 53% when obtained via a “blind” rectal swab. Culture performance, however, is similar regardless of swabbing technique.

Nucleic acid amplification tests (NAATs) are available for gonococcal detection in urethral, rectal and pharyngeal specimens. Although NAATs are not currently cleared by the Food and Drug Administration (FDA) for rectal or pharyngeal specimens, increasingly laboratories are offering such testing for these specimens.

Treatment

Data from the CDC’s Gonococcal Isolate Surveillance Project (GISP) 2004 indicate that fluoroquinolone-resistant N gonorrhoeae is more common among MSM than among heterosexual men (18% vs 2%). Therefore, fluoroquinolones should not be used for gonorrhea treatment among MSM, regardless of the site of infection.

Current STD treatment guidelines for urogenital gonococcal infection recommend a single 125-mg intramuscular injection of ceftriaxone, which cures 99.1% of uncomplicated urogenital and anorectal infections, or cefixime in a single 400-mg oral dose, which cures 97.1% of uncomplicated infections. If cefixime is not available, single-dose oral cefpodoxime, 400 mg, may be used. Empiric treatment for acute proctitis and proctocolitis syndromes consists of ceftriaxone, 125 mg intramuscularly, plus doxycycline, 100 mg orally twice a day for 7 days. This regimen offers coverage for the most common sexually transmitted pathogens that cause these symptoms (see Table 9–1) and is especially effective against N gonorrhoeae, Chlamydia, and incubating T pallidum.

Chlamydia trachomatis

Chlamydial infection is a cause of acute proctitis in MSM who practice receptive rectal intercourse. In a recent study of the etiology of clinical proctitis among MSM, 19% of 101 patients had chlamydial proctitis.

Clinical Findings

Symptoms and Signs

Rectal C trachomatis infections are usually asymptomatic or mildly symptomatic when caused by the non-lymphogranuloma venereum (LGV) strains of chlamydia. Non-LGV strains or serovars, usually genital immunotypes D or K, can cause a mild proctitis with symptoms of rectal discharge, tenesmus, or anorectal pain. In a recent prevalence study among MSM attending either an STD clinic or a Gay Men’s Health Clinic, 44 of 213 (21%) men with symptoms of proctitis had Chlamydia isolated compared with 272 (8%) of 3579 asymptomatic men. Regardless of symptoms, chlamydial infections of the rectum are usually associated with friable rectal mucosa and mucopurulent discharge as seen on anoscopy. Gram stains of rectal specimens show increased polymorphonuclear cells, even in asymptomatic patients. Sigmoidoscopy can be normal or can reveal mild inflammatory changes with small erosions or follicles in the lower 10–15 cm of the rectum.

In contrast, direct rectal inoculation with LGV strains (L1, L2, or L3) of C trachomatis may cause severe anorectal pain, a bloody mucopurulent discharge, and tenesmus in women and men who practice unprotected anal intercourse. Recent reports, however, suggest that some rectal LGV infections may be asymptomatic. A complete review of recent diagnostic recommendations for LGV infections can be found in Chapter 17.

Laboratory Findings

C trachomatis rectal infection may be confirmed by culture or by direct immunofluorescent stain. Enzyme immunosorbent assays for detection of chlamydial antigens in rectal samples have high false-positivity rates. NAATs have been used with good reported sensitivity and specificity, but no commercial product is currently FDA cleared for use with rectal specimens. At one time serologic testing was considered useful for the diagnosis of classic urogenital LGV, and a complement-fixation titer greater than 1:64 was considered suggestive of LGV infection, but data are incomplete, leading most experts to recommend against the use of serology in the diagnosis of rectal LGV infection.

Treatment

Doxycycline, 100 mg twice daily for 7–10 days, is effective in the treatment of non-LGV chlamydial proctitis and proctocolitis. Azithromycin, 1 g as a single dose, is effective for chlamydial urethritis and cervicitis and has been recommended for uncomplicated rectal infections. The recommended therapy for LGV infections is doxycycline, 100 mg twice daily for 21 days. Alternative regimens include erythromycin base, 500 mg orally four times daily for 21 days. Although azithromycin given as a 1-g oral dose once a week for 3 weeks may be effective, clinical data are lacking.

Treponema Pallidum

Primary and secondary syphilis rates declined steadily in the United States throughout the 1990s. Recently, however, these rates have begun to increase.

Clinical Findings

Symptoms and Signs

Primary syphilis can present as an anorectal chancre from 9 to 90 days after inoculation by an infected partner. Classically, the chancre is painless. If located in the perirectal area it may have well-demarcated indurated edges and a clean base. Although the chancre may be asymptomatic, patients may also present with itching, bleeding, rectal discharge, constipation, and tenesmus, and it may be easily misdiagnosed as a rectal fissure. If the primary chancre is located above the anal verge, within the anal canal, its appearance may be atypical. Patients with internal chancres may present with symptoms of pain on defecation or rectal bleeding, which may be mistaken for trauma, hemorrhoids, or neoplasms. Often these chancres go undetected unless digital rectal examinations and anoscopic evaluations are performed. Therefore, if the patient reports any anorectal symptoms and recent anorectal sexual activity, anoscopy should be included in the physical examination.

Lesions of secondary syphilis may also appear in the perirectal skin and rectal mucosa. Condylomata lata, which are generally smooth, heaped, wartlike lesions, or mucous patches are clinical manifestations associated with the secondary stage of syphilis. Condylomata lata may be easily confused with the more highly keratinized condylomata acuminata, but condylomata lata are usually moist, shiny, and smooth appearing, whereas warts are dry, dull, and rough appearing.

Laboratory Findings

Darkfield examination of fluid collected from any observed lesions in the perianal and anal region may be useful to immediately detect motile treponemes. If one typical treponeme is detected, the diagnosis of primary syphilis can be made. However, because 105 treponemes per milliliter are required for visualization, a negative test result does not rule out syphilis. Darkfield examination of rectal lesions is not helpful, as nonpathogenic treponemes can be found in the intestines and are easily confused with T pallidum. Because darkfield microscopy is not available to most primary care physicians, most diagnoses of anorectal syphilis are based on the physical examination and the results of serologic tests for syphilis.

Special Tests

Serologic tests for syphilis include the rapid plasma reagin (RPR) or the Venereal Disease Research Laboratories (VDRL) screening tests, which if positive, are confirmed by more specific tests such as the fluorescent treponemal antibody absorption (FTA-ABS) test or the T pallidum particle agglutination (TP-PA) assay. These tests may be nonreactive in 10–25% of patients with primary syphilis, if patients have not been infected long enough to mount a detectable antibody response. Some laboratories have begun to screen blood samples using treponemal EIA tests. Persons with a positive EIA screening test should have a standard nontreponemal test with titer to guide patient management decisions. For further discussion regarding EIA screening test interpretation, see Chapter 19.

Treatment

The drug of choice for primary and secondary syphilis remains 2.4 million units of intramuscular benzathine penicillin. Penicillin-allergic patients with primary or secondary syphilis can be treated with a 2-week course of doxycycline, 100 mg twice daily, regardless of HIV status. For further discussion, see Chapter 19.

Herpes Simplex Virus

Anorectal herpes infection is usually acquired by anal intercourse, but oral-anal contact with a partner who has orolabial herpes can also result in transmission. Most anorectal HSV isolates have been type 2 (HSV-2), but HSV type 1 also occurs. In a study of primary HSV proctitis, 70% of cases were caused by HSV-2 and 30% by HSV-1.

Clinical Findings

Symptoms and Signs

The clinical presentations of HSV infections are varied and range from asymptomatic to mild, moderate, or severe. The presentation of a primary first-episode infection, in which the patient has no serologic evidence of prior HSV-1 or HSV-2 infection and becomes infected with either type, may be severe. Primary anorectal HSV may involve the perianal skin and anal canal, and may extend to the rectum. Symptoms can include severe pain, with rectal discharge, tenesmus, and constipation. Nerve root S4–S5 dysesthesias, sacral paresthesias, urinary retention, and temporary impotence have been reported in up to 50% of patients with primary first-episode anorectal HSV infections. Patients may also have symptoms consistent with viremia such as fever, chills, malaise, headache, and meningismus. Symptoms and signs associated with recurrent disease tend to be milder, as with other forms of genitourinary HSV infections, and are not typically accompanied by urinary retention or impotence.

On examination of the perianal area, typical herpetic vesicles, pustules, or ulcerations may be seen. In severe cases, perirectal edema and erythema may be confused with a yeast infection. Anoscopic examination may be painful and may reveal an edematous, friable mucosa with ulcerations. In immunocompetent individuals, the infection rarely extends above 15 cm.

Laboratory Findings

Culture or direct immunofluorescent stains confirm the diagnosis. PCR testing may be used for diagnosis of perianal lesions.

Treatment

In a prospective, double-blind, placebo-controlled trial evaluating therapy for primary HSV proctitis, acyclovir, 400 mg orally taken five times daily for 10 days, was clinically efficacious compared with placebo. No other controlled trial has been conducted recently, but some experts believe that acyclovir, 400 mg orally three times daily, valacyclovir, 1 g orally twice daily, and famciclovir, 250 mg orally three times daily—all given for 7–10 days—can be administered according to the same recommended dosing schedules as for other first-episode genitourinary HSV infections.

HIV-infected patients or other immunocompromised patients can present with severe mucocutaneous HSV. These patients should receive 5–10 mg/kg of intravenous acyclovir every 8 hours until clinical improvement is attained. Patients may be placed on oral HSV suppression using acyclovir, 400 mg twice daily. A double-blind, placebo-controlled, crossover trial of famciclovir, 500 mg orally twice daily, versus placebo for 8 weeks reported clinically and statistically significant reductions in the symptoms associated with HSV infection and in the symptomatic and asymptomatic shedding of HSV among HIV-infected persons.

Enteric pathogens cause infections that are associated with the ingestion of fecally contaminated food or water. However, certain sexual practices, especially anilingus, may allow direct exposure to these pathogens. These sexual behaviors can promote transmission of Campylobacter, Shigella, Salmonella, Entamoeba histolytica, Giardia, and several other enteric pathogens, which may result in symptoms of proctocolitis or gastroenteritis, or both.

Shigella

Shigella is the third most common cause of bacterial gastroenteritis in the United States, with the majority of cases occurring among young children and their caretakers. However, increases in Shigella infection among adult men were recently reported, attributable to outbreaks among MSM.

The infective dose for shigellosis is very small (10–100 organisms), and transmission can occur rapidly. An infected individual can be very contagious. Therefore, whenever Shigella is detected by a diagnostic laboratory, it is immediately reported to the local public health department and the infected individual is contacted for immediate therapy and interview.

Clinical Findings

Clinically, patients with Shigella infections may present with an array of symptoms. Symptoms may be absent or may include abrupt onset of watery or bloody diarrhea with associated nausea, tenesmus, cramping, and fever. Rarely, toxic megacolon has been reported as a complication of infection. Examination of stool shows red blood cells and mucopus, and sigmoidoscopy may reveal an inflamed, friable mucosa extending above 15 cm. Diagnosis is confirmed by stool culture on selective media.

Treatment

Treatment is supportive and consists mainly of hydration. Antimotility agents should not be given. Antibiotics are not recommended to treat shigellosis in otherwise healthy patients, and their use should be reserved to prevent complications in immunocompromised patients. If given, antibiotics should be selected according to regional antibiotic sensitivities because of widespread development of resistance. Ciprofloxacin, 500 mg orally twice daily for 5–7 days, has been reported as effective therapy. In severely ill patients receiving antibiotic therapy, stool and blood cultures should be repeated to monitor therapeutic response, because antibiotic resistance may develop and recurrences are common. Contact tracing to detect asymptomatic carriers is an important public health measure, but the value of treating sexual contacts is unknown.

Salmonella

Although Salmonella has been reported as a cause of proctocolitis and enterocolitis in homosexual men, its impact is most significant among AIDS patients, in whom a 20-fold increased incidence is noted. Salmonella bacteremia in an HIV-infected person is diagnostic of AIDS. Infections in immunocompromised individuals, usually due to Salmonella typhimurium and Salmonella enteritidis, are frequently associated with bacteremia that recurs despite directed therapy.

Diagnosis is made by culture of stool on selective media. Treatment is individualized according to symptom severity and antibiotic sensitivity. In immunocompetent patients with mild illness, supportive therapy without antibiotics is usual. In AIDS patients with Salmonella infection, ciprofloxacin, 750 mg twice daily for 2–4 weeks, is generally recommended, and ciprofloxacin, 500 mg, is given indefinitely if relapse occurs.

Sexual transmission as a mode of spread for parasitic infections was suggested in 1972. The prevalence of Giardia lamblia and Entamoeba histolytica has been reported to be as high as 30–40% in selected populations of MSM and correlates better with a history of anilingus than with travel to endemic areas.

Giardia Lamblia

G lamblia is usually a waterborne disease but can be sexually transmitted through anal-oral contact. Because it is typically an infection of the small intestine, it can cause symptoms of enteritis. Symptoms include diarrhea, bloating, abdominal cramps, and nausea. Multiple stool examinations are often required to document infection with G lamblia. When stool examination findings are negative, sampling of jejunal mucus by the Enterotest or by small bowel biopsy confirms the diagnosis.

Therapeutic choices include metronidazole, 250–500 mg orally three times daily for 7 days, but this regimen is associated with a 10–20% failure rate. Tinidazole, given as a 2-g oral single dose, is recommended for giardiasis, and nitazoxanide, 500 mg orally twice daily for 3 days, is a new thiazolide antiparasitic agent with excellent activity and tolerance. Older regiments include paromomycin, 500 mg orally three times daily, or furazolidone, 100 mg four times daily for 7–10 days.

Entamoeba Species

Two distinct species of Entamoeba, a pathogenic form (Entamoeba histolytica) and a nonpathogenic form (Entamoeba dispar), can cause gastrointestinal infection. These forms are morphologically identical.

E histolytica has been found in the stool of both symptomatic and asymptomatic individuals. If symptoms are present, they can vary from mild diarrhea to fulminant bloody amebic dysentery. Amebic proctocolitis and other inflammatory bowel diseases have the same appearance on colonoscopy. Diagnosis is best confirmed by the identification of E histolytica cysts or trophozoites on examination of fresh stool specimens, although PCR tests have been developed for both parasites.

E dispar is considered nonpathogenic, and identification of this form is clinically significant because the patient may not need therapy. Until recently, the inability of microscopy to distinguish between the two ameba species, and the time it takes to culture and subsequently differentiate Entamoeba by isoenzyme analysis, made specific diagnoses difficult, but the development of highly sensitive and specific PCR techniques has simplified diagnosis.

If E histolytica is identified in screening specimens of asymptomatic individuals, therapy is given to prevent continued infection and avoid transmission. Recommended therapy is with the luminal amoebicide, iodoquinol, at a dose of 650 mg orally three times daily for 20 days. Alternative regimens include paromomycin, 25–30 mg/ kg/day orally in three doses for 7 days, or diloxanide furoate, 500 mg orally three times daily for 10 days; the latter is only available through the CDC. Metronidazole, 750 mg orally three times daily for 10 days, is the treatment of choice for invasive, symptomatic infection. This regimen, however, does not eradicate organisms in the intestinal lumen and must be followed by a course of iodoquinol in the dose indicated above.

Entamoeba nana, Entamoeba coli, and Entamoeba hartmanni have frequently been identified in the stool of homosexual men. Iodamoeba butschlii and Dientamoeba fragilis are less commonly identified, and the significance of any of these parasites as potential pathogens has not been established. Several protozoan parasites, which include Cryptosporidium, Isospora, Cyclospora, and Microsporidia, have been reported among AIDS patients with severe and sometimes unrelenting diarrhea. The epidemiology of these infections is not fully understood, and the role of sexual transmission has not been studied but should be addressed in future research.

• • If a patient reports any anorectal symptoms and recent anorectal sexual activity, anoscopy should be included in the physical examination.