This time-series study encompassing EHR’s reported cases of STI in primary care in Catalonia found a global decrease of 20.2% of the expected monthly incidence of STI in the 2020–2021 analysis period compared to the expected. This reduction was greater during the lockdown period (up to 39%). The most affected groups were women, people under the age of 60 years, less deprived urban areas and some types of STI (chlamydia, gonorrhoea and HIV).
Comparison with existing literature
Several studies reported a decline in new STI diagnosis during the lockdown period probably related to the impact of social distancing measures [9, 10, 14, 15, 18–20]. In addition, some studies described a reduction in the number of casual sex encounters [21, 22], although others showed a stable number or even an increase in some high-risk sexually active populations . On the other hand, many countries in the WHO European Region reported severe disruptions in test provision (up to more than 50% decline in testing volume) due in part to testing site closure, reduced attendance, laboratories overburdened, etc .
Overall, Chlamydia genital infection was the STI with the greatest reduction in our study. This finding was higher than the under 20% reported in literature [9, 15, 20]. In Spain, a multitest including gonococcal, chlamydia, mycoplasma genitalium and trichomonas infection is available in primary care centres. This may explain the concordance of reduction in chlamydia and gonococcal infections, with a higher decline in the first one due to a higher number of asymptomatic cases detected by screening measures that were halted during the lockdown period. However, some European countries did not find relevant changes in incidence  or attendance  for chlamydia or gonococcal infections, maybe due to lesser restricted social and travel measures . Gonococcal genital infection showed disparities in previous studies with a wide range from increased incidence [9, 14, 20, 26] (up to 56% in Taiwan ) to reduced new diagnoses[9, 15, 18] (up to 36,9% reduction in Greece ).
In Melbourne, despite keeping usual care in sexual centres, a reduction of 40% in attendees, 65% in screening or 40% in non-gonococcal urethritis was found during the lockdown period (23 March to 10 may 2020) compared with the previous months of the year. However, non-significant differences were observed in such STI with marked symptoms, like syphilis or pelvic inflammatory disease. In our study, the STI with lesser reduction was syphilis. This result is consistent with other data reported elsewhere, showing little increased figures and reductions of less than 10% in syphilis trends [9, 14, 18, 20]. This may suggest that people presenting more severe clinical conditions seek medical attendance, leading to a specific STI diagnosis . Another reason could be that extragenital or skin transmissible lesions of syphilis escape from the use of barrier methods to prevent STI, compared with urethral discharge characteristic of gonorrhea, which had shown greater reductions than syphilis in the context of the COVID-19 pandemic [19, 20]. In addition, non-specific STI and urethritis were the only STI that rose above the expected during the post lockdown period; except in January 2021 for urethritis, coinciding with a third wave of coronavirus disease in Catalonia. Probably, restrictions affecting both laboratory and PCP’s accessibility could lead to an increase of non-specific diagnoses at the expense of an underreporting of etiologic STIs.
HIV was underdiagnosed in consonance with published data [14, 15, 20] or persistently allocated in the low expected confidence interval during the three periods analysed in 2020–2021. Regardless of the small number of HIV cases, it deserves special attention due to the burden of the disease. In the near future, special efforts should focus on monitoring whether there will be a rebound or greater diagnostic delay in new HIV cases, hindering the achievement of the 90-90-90 WHO goals for HIV infection [27, 28].