What human papillomavirus (HPV) type is a 26-year-old woman with high-grade squamous intraepithelial lesions (HSIL) on her Pap (Papanicolaou) smear most likely infected with?

HPV Type Most Likely Associated with HSIL in a 26-Year-Old Woman

HPV 16 is the most likely type of human papillomavirus causing high-grade squamous intraepithelial lesions (HSIL) in this 26-year-old woman with multiple risk factors.

Epidemiology and Association of HPV Types with HSIL

HPV 16 is strongly associated with HSIL and cervical cancer development for several reasons:

• HPV 16 accounts for approximately 50-60% of invasive squamous cell carcinomas worldwide 1
• In patients with HSIL, HPV 16 is detected in 53.1% of cases, making it the most common HPV type found in high-grade lesions 2
• HPV 16 is uniquely associated with cervical intraepithelial neoplasia Grade 3 or worse (CIN3+), is most likely to persist, and has the highest probability of progressing to higher-grade lesions 1
• The prevalence of HPV 16 is significantly higher in HSIL (60.7%) compared to lower-grade abnormalities like LSIL (23.6%) and ASC-US (13.3%) 1

Risk Factors Present in This Patient

This 26-year-old woman has several risk factors that increase her likelihood of HPV 16 infection and HSIL:

• Multiple sexual partners since age 18
• Tobacco use disorder (smoking is a known cofactor for HPV persistence and progression)
• Lack of gynecologic care for over 5 years (missed opportunity for early detection)

HPV Types and Their Association with Cervical Lesions

Different HPV types have varying associations with cervical lesions:

• HPV 16,18,31,33: High-risk types associated with HSIL and cervical cancer

  • HPV 16: Most common in HSIL (53.1%) 2
  • HPV 18: Found in 10.3% of HSIL cases 2
  • HPV 31/33: Found in 8% of HSIL cases 2

• HPV 6,11: Low-risk types primarily associated with genital warts and rarely with HSIL

  • Only found in 2.96% of HSIL cases 2
  • Progression to HSIL is not found in patients with low-risk HPV 6 and 11 infection 3

Clinical Implications

The identification of HPV 16 in this patient has important clinical implications:

• The CDC recommends colposcopy for any HPV 16 or 18 positive result regardless of cytology due to the significantly increased risk of cervical precancerous lesions 4
• Women infected with HPV 16 have more frequent progression of lesions to higher-grade HSIL and should be intensively monitored because of the increased risk for development of cervical carcinoma 3
• HPV 16 carries a 17-21% risk for CIN3+ development, which is significantly higher than other HPV types 4

Diagnostic Considerations

While HPV testing is highly valuable, there are important caveats to consider:

• A small percentage (8.3%) of HSIL cases can be HPV negative despite histological confirmation 5
• Type-specific viral load may be a powerful diagnostic marker for HSIL+ in HPV 16-infected lesions 6
• HPV negative HSIL is more common in older women (mean age 49.3 years) compared to HPV positive HSIL (mean age 40.7 years) 7

Given the patient's age, risk factors, and HSIL finding on liquid-based cytology, HPV 16 is the most likely causative agent in this case.