Discussion

Incidence and risk factors:

Gonorrhea is a mandatory reportable disease to the CDC. Their latest data, published in 2019, yielded the incidence of Gonorrheal infections in the United States.

For the male risk factor, based on CDC data the rate of infections in the US is 224.4 cases per 100,000, which was used to calculate the likelihood ratio vs. the general population. Similarly, the rate for those aged 15 – 24 was 593.7 cases per 100,000, which was used to calculate the likelihood ratio vs. the general population.

The likelihood ratio for MSM was calculated similarly, with a rate of 5,165.6 per 100,000 which would result in an LR of 29. The LR was reduced to attempt to correct for the overlap of MSM and HIV which is the next risk factor listed. Of note, this is significantly higher than the previous risk factors of male and teenage / young adult. The CDC does note that rates among MSM population increased dramatically between 2013 – 2018 but decreased from 2018 – 2019. They note this could represent truly a higher case rate among MSM during this time period, or an increase in case ascertainment due to increased asymptomatic screening and screening of extra genital sites.

For people living with HIV (PLWH), a recent study by Li et al published in Clinical Infectious Diseases demonstrated 2.88 per 100 person years of PLWH had gonorrheal infections.[2] Using this number, the likelihood ratio was calculated to be 15, and further reduced as above to account for the overlap with MSM.

Symptoms/Syndromes:

The likelihood ratio for PID was taken from Reekie et al who examined gonorrhea and chlamydia testing in those presenting to a hospital and diagnosed with PID in Australia.[3]

Lusk et al demonstrated that of patients diagnosed with cervicitis, 1.1% were positive for gonorrheal infections, which was used to calculate the likelihood ratio. [4]

Taylor et al demonstrated that of male patients diagnosed with urethritis, 21.6% were positive for gonorrheal infections, which was used to calculate the likelihood ratio.[5] The LR was adjusted to account for multiple risk factors.

Hamlyn et al demonstrated that of MSM patients diagnosed with proctitis, 30% were positive for gonorrheal infections, which was used to calculate the likelihood ratio.[6] The LR was adjusted to maintain internal validity with the remainder of the calculator.

Test sensitivity & specificity:

Sensitivity data for NAAT for gonorrhea was dependent on anatomic site being tested, with a range of 84% for oropharyngeal infections to 93% for rectal infections during asymptomatic screening. Rates were higher in symptomatic infections.[7]

Although rarely performed, published data for gram stain sensitivity is high (90% or higher in urethral smears). This is lower for other anatomic sites (down to 50 – 70% for endocervical smears). The specificity has been reported as high (greater than 90%), but more recent data demonstrates that this may be as low as 60% due to detection of Neisseria meningitidis.[8]