Which bacteria are most commonly transmitted or encountered during anal intercourse?

Bacteria Commonly Transmitted During Anal Intercourse

The most common sexually transmitted bacterial pathogens encountered during anal intercourse are Neisseria gonorrhoeae, Chlamydia trachomatis (including lymphogranuloma venereum serovars), and Treponema pallidum (syphilis), which cause proctitis in the distal 10-12 cm of the rectum. 1, 2

Primary Bacterial Pathogens in Receptive Anal Intercourse

The CDC guidelines consistently identify four main sexually transmitted pathogens affecting the anorectum:

• N. gonorrhoeae causes anorectal infection predominantly through receptive anal intercourse, presenting with anorectal pain, tenesmus, and rectal discharge 1, 2
• C. trachomatis (including LGV serovars) is transmitted via genital-anal mucosal contact and increasingly affects HIV-negative men who have sex with men 1, 2
• T. pallidum (syphilis) affects the perianal skin and distal anal canal, producing symptoms similar to genital syphilis 1, 2
• Mycoplasma genitalium should now be considered in symptomatic proctitis after excluding the above common pathogens 2

Critical caveat: The majority of rectal chlamydia and gonococcal infections are asymptomatic and can only be detected by laboratory testing, making routine screening essential for anyone with a history of receptive anal contact 2, 3

Enteric Bacteria in Insertive Anal Intercourse

For men who are the insertive partner during anal intercourse, a different bacterial spectrum emerges:

• Escherichia coli and other enteric gram-negative organisms can cause sexually transmitted epididymitis in the insertive partner 1, 4
• This occurs through exposure to enteric flora during insertive anal intercourse 1

Bacteria Causing Proctocolitis (Beyond 12 cm)

When inflammation extends beyond the rectum (>12 cm), additional bacterial pathogens are involved:

• Campylobacter species cause proctocolitis with diarrhea and abdominal cramps 1
• Shigella species are transmitted via oral-anal contact and cause proctocolitis or enteritis 1, 2

Clinical Presentation Patterns

Acute proctitis (limited to distal 10-12 cm) presents with:

• Anorectal pain, tenesmus, and rectal discharge 1
• Anorectal pus or polymorphonuclear leukocytes on Gram stain 1

Proctocolitis (extending beyond 12 cm) adds:

• Diarrhea and/or abdominal cramps 1
• Fecal leukocytes on stool examination 1

Diagnostic Approach for Recent Receptive Anal Intercourse

Patients with acute proctitis and recent receptive anal intercourse require:

• Anoscopy examination to visualize anorectal inflammation 1
• Testing for HSV, N. gonorrhoeae, C. trachomatis, and T. pallidum 1
• Gram stain of anorectal secretions if anorectal pus is present 1
• Stool examination and culture if symptoms suggest proctocolitis 1

Empiric Treatment Before Culture Results

When anorectal pus or polymorphonuclear leukocytes are found, immediate empiric therapy should include:

• Ceftriaxone 125 mg IM (for gonorrhea coverage) 1
• PLUS Doxycycline 100 mg orally twice daily for 7 days (for chlamydia coverage) 1

This regimen covers the two most common bacterial causes while awaiting definitive test results 1

Important Clinical Pitfalls

Do not assume condom use provides complete protection - bacterial STIs are often spread without penile penetration through digital-anal contact and toys 2, 3

Do not overlook asymptomatic infections - screening is indicated for anyone with a history of receptive anal contact, regardless of symptoms, as most rectal chlamydia and gonorrhea infections are silent 2, 3

Consider LGV in severe or persistent proctitis - lymphogranuloma venereum serovars of C. trachomatis are increasingly found in HIV-negative MSM and require extended treatment 2

Evaluate sexual partners - all sexual contacts should be examined and treated to prevent reinfection 1