The present study describes the most recent epidemiology of bacterial meningitis and IMD in Colombia. The key findings of the study are: (1) IMD and other bacterial meningitis cases decreased in 2020 and 2021 relative to 2015–2019; (2) IMD incidence and IMD mortality incidence (per 100,000 population) were highest among infants aged < 1 year, followed by children aged 1–4 years; (3) since 2015, serogroup C has been responsible for the majority of IMD cases, overall and in each age group; (4) Bogotá and Antioquia had the highest numbers of IMD cases, while Risaralda and Bogotá had the highest incidences of IMD (per 100,000 population); and (5) low–low SE status neighborhoods had the highest burden of IMD (cases and deaths) and the shortest median hospital stay.

We report cases of confirmed bacterial meningitis for 2015–2017, but cases of confirmed bacterial meningitis or other IMD for 2018–2021, as that is what was included in the event reports [14,15,16,17,18,19,20]. Laboratory surveillance results show that 66% of IMD cases during 2015–2017 were meningitis, 24% were sepsis, and 10% were other IMD [22], hence Fig. 1 is missing a number of cases of non-meningitis IMD during 2015–2017. Regarding the lower numbers of IMD cases during 2020 and 2021 compared to 2018–2019 (52 and 32 vs. 108–116), this was likely due to non-pharmacological measures that were implemented to prevent the spread of coronavirus disease 2019 (COVID-19), e.g., reduced social contact and face masks, which also reduced the spread of N. meningitidis and other pathogens [19, 20]. However, following the relaxation of these measures, cases of IMD and other transmissible diseases are likely to increase [8]. Indeed, there were 54 confirmed cases of IMD in Colombia in 2022 [34] and 64 cases in the first 32 weeks of 2023 (i.e., 104 over the year if a constant rate is assumed) [35].

In the current study, most IMD deaths (among confirmed cases) were in children aged < 10 years (34.6%), followed by 10–19 years (22.0%), then ≥ 60 years (15.0%). Colombian data from 2005 to 2011 also showed that most IMD deaths (among probable cases) were in young children (< 5 years: 29%), but it is difficult to compare our results to the earlier data as their age groupings were different, so 44% of IMD deaths were among people aged 15–59 years, but this includes a large proportion of the population [13].

In the US, meningococcal vaccination is targeted towards adolescents and at-risk individuals [36]. Adolescents tend to have the highest rates of nasopharyngeal carriage (e.g., 23.7% of 19-year-olds in a 2010 meta-analysis [37]), increasing the risk of transmission within and from this age group. Vaccinating adolescents can therefore also help to protect other age groups [7, 8]. However, meningococcal nasopharyngeal carriage studies in Colombia have reported much lower carriage rates of 6.9% among 15–21-year-olds in Bogotá in 2012 [38] and 1.9% among 11–25-year-olds in Cartagena in 2019 [39]). In the current study, the highest burden of IMD during 2010–2021 was seen among infants aged < 1 year, with a mean incidence of approximately 1 per 100,000 and a mean mortality of around 0.3 per 100,000. This was followed by children aged 1–4 years, in whom the mean incidence was around 0.2 per 100,000 and mortality was approximately 0.1 per 100,000. Therefore, in Colombia, a vaccination strategy mainly targeting infants and young children is likely to be most beneficial to prevent IMD-related disability and death. Infant vaccination has already been implemented in various countries, including Chile (MenB and MenACWY) [10], Cuba (MenBC) [6], Brazil (MenC routinely, but MenACWY for high-risk infants) [6], and Argentina (MenACWY), which also recommends adolescent MenACWY vaccination [9].

Serogroup B was the dominant serogroup in Colombia until 2014, but serogroup C was dominant in all age groups examined during 2015–2020. The high numbers of serogroup C IMD cases during 2016–2019 (Fig. 5) may be due to continuous outbreaks. Serogroup B continues to be responsible for various outbreaks in Colombia, including six IMD cases in 2012 in children (aged 1.5–11 years) in a low-income neighborhood in Cartagena, of whom three died [40]. These cases were associated with estimated costs of US$735 for outbreak control, $3,935 for disease surveillance, and $4,921 for hospital care (tests, intensive care unit, regular ward, drugs, and procedures) (2011 US dollars) [40]. There have also been other documented outbreaks of serogroup B IMD in children and adolescents in Cartagena during 2010–2015. A later serogroup B outbreak affected three children (aged < 5 years) in Magdalena in 2018 [41]. This was managed by vaccinating 49 direct contacts and giving prophylaxis to 69 health personnel [41]. Six small outbreaks were reported by INS in 2018 in six different departments [17]. There were four serogroup C and two serogroup B outbreaks. Three were in military forces, two in the community, and one in a prison [17]. A further eight small outbreaks were reported by INS in 2019, of which three were serogroup C, three serogroup Y, and two unknown [18]. Four of these occurred in the military, two in the community, one in a prison, and one in a migrant population [18]. Soumahoro et al. [42] recently concluded that emergency mass vaccination in response to outbreaks was costly, and hampered by difficulties obtaining sufficient doses, issues with consent, and poor uptake; hence routine meningococcal vaccination is an attractive alternative. In Colombia, this could perhaps best be targeted to the departments with the highest IMD incidences and to low SE status areas in order to reduce the public health and social impact of IMD.

Serogroup Y was very infrequently detected in Colombia before 2003, but in 2006, it was the most common serogroup detected (Fig. 5), likely due to an outbreak among adolescents. Interestingly, although the numbers of cases of serogroup B and C decreased dramatically from 2019 to 2020/2021, serogroup Y did not decrease, which increased its relative importance (Fig. S2 in the Supplementary Material). Serogroup Y has also been the most common serogroup during the first 32 weeks of 2023 [35].

Unfortunately, molecular characterization of IMD isolates is not included in the Colombian surveillance program [43]. However, a study of 25 serogroup B isolates from Cartagena during 2012–2014 reported that 68.0% were B:10,15:nt phenotype associated with clonal complex ST-41/44, with various other phenotypes making up the remainder [44]. Another study of 193 Colombian IMD isolates from 2013 to 2016 reported that serogroup C and B were dominant (47.9% and 41.7%, respectively), with serogroup Y accounting for 9.4% [45]. A total of 15 clonal groups were identified [of which serogroup B sequence type (ST)-9493 was most common) and 14 clonal complexes (cc) (mainly ST-11 cc, ST-32 cc, ST-35 cc, and ST-41/44 cc) [45]. Further study of the 34 serogroup B ST-9493 isolates showed that the most common alleles were porin A 17 and porin B 44, while the most common peptides were factor H binding protein (fHbp) 2.24 and neisserial heparin binding antigen 10 [43]. It may be beneficial to perform genomic surveillance in Colombia in order to detect new clones [43]. The Sociedad Latinoamericana de Infectologia Pediatrica (SLIPE; Latin American Society of Pediatric Infectology) has recently highlighted the importance of active surveillance of IMD cases, along with recommending carriage and pharmacoeconomic studies and potentially the use of vaccines [8].

Regarding IMD cases by department during 2010–2021, Bogotá and Antioquia had the highest numbers of IMD cases (179 and 122, respectively), accounting for over half of the cases during that time, and some of the highest 12-year incidences (2.41 and 1.90 per 100,000, respectively). This is not surprising, as Bogotá is Colombia’s densely populated capital and has most of the healthcare facilities, while Antioquia is home to the large urban city of Medellin. Bolivar and Risaralda had similar 12-year incidences (2.37 and 2.44 per 100,000), but had much lower numbers of IMD cases (only 49 and 23, respectively).

In the SE status analysis, for which Cartagena was chosen because of the 2012 outbreak in this city [40], the low–low SE status neighborhoods had the highest number of IMD cases, the most IMD deaths, and the highest lethality, but the shortest median hospital stay (which approached significance for low–low/low vs. medium–low). Over half (52.2%) of the IMD patients from low–low SE neighborhoods died after a maximum of 3 days of hospitalization, which could reflect limited access to healthcare and a longer time with symptoms and disease progression before accessing healthcare, thus increasing the severity of the outcome. Indeed, income-related inequalities in barriers to seeking health services have previously been reported to be higher in Colombia than in three other Latin American countries (El Salvador, Paraguay, and Peru) [46]. The medium–low SE status neighborhoods had a lower lethality and a longer median hospital stay, which could imply that people in these neighborhoods sought healthcare more quickly. Interestingly, a previous study in Colombia reported that departments with higher inequality had significantly higher meningitis incidences [47]. Studies in England have also shown that deprivation is associated with increased risk of meningococcal disease [48, 49]. Overall, these differences imply disparities in access to healthcare and inequity by SE status that deserve to be addressed.

The World Health Organization and the Pan American Health Organization both recently launched roadmaps to defeat/curb meningitis by 2030, due to its potentially devastating sequelae and high lethality [50, 51]. The aims include the elimination of bacterial meningitis epidemics and a reduction in vaccine-preventable bacterial meningitis cases [50, 51]. Suggestions include new affordable vaccines, high immunization coverage, and improved disease surveillance [50]. The latter was also highlighted for strengthening in Latin America in 2015, with a focus on improving laboratory capabilities, communication, etc. [52]. Of note, IMD incidences in Colombia using data from laboratory surveillance were consistently lower than those from event reports. However, the difference seemed to improve over time, potentially reflecting improvements at both system and laboratory testing levels.

There are a number of limitations that are inherent to surveillance systems, especially passive ones, including underreporting, lack of representativeness, and lack of timeliness [53]. According to national guidelines, all IMD samples captured by the national surveillance (i.e., SIVIGILA) should be sent to a laboratory for testing [54]. However, IMD incidences were lower by laboratory surveillance than by event reports, showing that there is room for improvement in Colombia, which could help to strengthen surveillance and evaluate the impact of interventions. Given this discrepancy, we requested certain data from the INS under the law of transparency to cross-check and validate the data from the publicly available reports. We also noted various inconsistencies within and between the various reports, which could be either editing errors or missing data. There were also some data that we were unable to obtain.

For the SE status analysis, the sample might be biased towards more severe IMD patients who required healthcare and hospital admission, and mild cases might not be captured. It was also difficult to compare IMD across the whole range of SE status neighborhoods as there were no IMD cases in medium, medium–high, or high SE status neighborhoods, although it should be noted that < 10% of the population lived in such neighborhoods in Cartagena. Lastly, clinical data were extracted primarily from medical histories.