A large proportion of cervical, rectal, and oropharyngeal gonococcal infections are asymptomatic (10,11). Detection of asymptomatic infections depends on screening (12,13). It is possible that there could have been reductions in the frequency of asymptomatic screening or the size of the screened population—and hence lower detection of gonorrhea—which could be due to patient behavior and to clinical practice.

Are individuals presenting for screening less frequently, resulting in fewer diagnoses? The lockdowns and home isolation associated with COVID-19 in 2020 and, to a lesser degree in 2021, reduced screening frequency and raised test positivity (14,15). Surveillance data indicate a dip in both chlamydia case rates (Figure 1) and the male-to-female ratio of case rates of chlamydia and gonorrhea (Figure 2), suggesting that any pandemic effects – such as changes in screening or sexual behavior – were more pronounced in men than in women. Gonorrhea diagnoses did not decline until 2022 and 2023. As any behavior change during the COVID-19 pandemic should have had an immediate effect on incidence, reduced screening in 2020 is an unlikely cause for the subsequent observed gonorrhea declines. Moreover, the rates of chlamydia were stable in 2022-23, whereas reduced screening would impact reporting of both gonorrhea and chlamydia, as specimens are typically tested for both conditions simultaneously (14).

Are clinical providers screening fewer patients (narrowing the eligibility criteria for screening) or screening those who are eligible less frequently? Recently, a call to reconsider the effectiveness of screening for chlamydia and gonorrhea in MSM gained a growing chorus of voices, motivated by concerns about antimicrobial resistance and limited health benefits (16-19). It is unclear to what extent there has been a change in US screening practice. Gonorrhea and chlamydia are more common in specific subpopulations—MSM and heterosexual populations, respectively—and differences in case rates might be due to varying screening practices. However, since 2021, the case rate of gonorrhea decreased most rapidly among women aged 20-29 (1), for many of whom screening is still encouraged (annually for women under 25 and women over 25 with risk factors) (20) and who exhibit higher rates of chlamydia than gonorrhea. National data on testing volumes, stratified by age, sex, sex of partners, geography, symptom status, and reason for testing, would help clarify this hypothesis.

The vast majority of diagnoses in the US are made by nucleic acid amplification tests (NAATs) from a range of manufacturers (21). Access to at-home sample collection for STI testing is expanding (22). At home-collection performs as well as clinician collection in office settings when subjected to NAATs (22,23). Changes in the fraction of samples collected at home should not impact the overall diagnosis rate, unless there is differential reporting of results from at-home tests or sample collection. Diagnostic platforms providing test results at home are not yet widely available (24), yet surveillance systems should prepare to track their use and ensure equal reporting of at-home diagnoses to measure impacts on STI reporting.

Has the pathogen evolved to escape diagnostics? Gonorrhea NAATs require the presence of a fragment of DNA or RNA with a specific nucleotide sequence. In several instances, N. gonorrhoeae evolved to escape these diagnostics by dropping or altering the targeted genetic fragment (25,26). To produce the simultaneous decline in gonorrhea diagnoses in three of four census regions (1), the diagnostic escape mutation would have to affect an assay commonly used in all three regions and would have had to emerge in multiple locations or spread very rapidly (27), which seems unlikely. Diagnostic escape would also be associated with more reports of persistent symptoms without known cause. Nevertheless, this hypothesis could be evaluated by comparing test positivity across testing platforms, which target different nucleotide sequences. Whole genome sequencing to determine changes in the targets of NAATs among culture-positive gonorrhea cases may help further assess the diagnostic escape hypothesis.

The simplest potential explanation may be that there was a shift in the completeness of case reporting – for example due to changes in the local public health workforce – that varies geographically, given that the decline in gonorrhea incidence was reported in the South, Midwest, and West, but not the Northeast census regions (1). However, it seems unlikely that reporting completeness would drop only for gonorrhea and not for other bacterial STIs, especially since the adoption of electronic case and laboratory reporting across the US in recent years has led to more complete reporting of notifiable diseases (28). Changes in case definitions of notifiable diseases would have had a national effect (29). One approach to assessing this possibility is to quantify the trends in test volume and positivity by state and by census region.

The frequency of sexual encounters and the number of sexual partners decreased during the first years of the COVID-19 pandemic (30-33). Yet while chlamydia case rates fell sharply in 2020, gonorrhea did not decline until 2022 and 2023, at which point chlamydia case rates had stabilized (Figure 1). Syphilis case rates continued to increase through the pandemic period. It is unclear which mechanisms led to the divergence of gonorrhea and chlamydia case rates from 2020 onwards, though groups with varying prevalence of each STI could have adjusted their sexual behavior in different ways; more behavioral data are needed to evaluate this hypothesis.

Clade II of the mpox virus began spreading globally in May 2022, with over 33,000 cases reported in the US by August 2024, mostly in MSM (34,35). The mpox epidemic contributed to lowering sexual contact rates and raising the use of barrier methods, largely in 2022, though behavior changes continued into 2023 (36,37). Yet, this mechanism is at odds with increasing rates of STIs, including gonorrhea, outside the US, notably in Europe (38), where similar patterns in behavior change in response to the mpox outbreak were observed (36). We would also expect mpox-associated behavior change among MSM to impact gonorrhea case rates in men more than in women, but the decline in gonorrhea was most pronounced in women (1).

The age of sexual debut is increasing and the number of partners among adolescents and young adults is declining (39). Young adults aged 20-24 also had a rapid decline in gonorrhea diagnosis rates in 2022-23 and saw a 2.8% drop in chlamydia cases among women in 2023 (1). While the proportion of youth who initiated sexual activity before turning 13 declined more rapidly among MSM than men with opposite sex partners from 2015-19 (39), more data are needed on relative changes in age of sexual debut by sex and sex of partners and on how these changes relate to differences in diagnosis rates. Other changes in sexual behavior, including involvement of specific anatomic sites or engagement in risky behavior, could also impact STI incidence (40). Prevalence estimates, behavioral surveys, test volume, and data on co-infections with detailed stratifications may help illuminate the role of behavior changes in explaining declining gonorrhea case rates.