Sentinel Surveillance for Pediatric Bacterial Meningitis in a Tertiary Level Pediatric Hospital in Colombia, 2016 - 2023

This 2016–2023 sentinel surveillance study at a Colombian tertiary pediatric hospital characterized the epidemiology, clinical presentation, and etiology of bacterial meningitis in children under five, revealing that *Streptococcus pneumoniae* (predominantly non-PCV10 serotypes) and *Haemophilus influenzae* type b were leading causes with a significant burden on infants under two years and a mortality rate of 11.6%.

The Gist

Imagine the human brain as a very sensitive, high-tech computer server room. Bacterial Meningitis is like a group of tiny, destructive hackers (bacteria) breaking into that server room, causing a massive fire alarm (fever), short-circuiting the system (seizures), and potentially crashing the whole computer (death or permanent damage).

This paper is a report card from a "Sentinel Hospital" in Colombia (a special hospital that acts like a watchtower) between 2016 and 2023. The doctors there kept a close eye on all the little kids (under 5 years old) who came in with symptoms of this infection to see who the hackers were, how bad the damage was, and if the "security software" (vaccines) was working.

Here is the story of what they found, broken down simply:

1. The Watchtower Mission

The hospital, called HOMI, is a top-tier pediatric hospital in Bogotá. They didn't just wait for patients; they actively looked through their records to find every child suspected of having this infection. Think of them as detectives sorting through a massive pile of "missing person" reports to find the real cases.

• The Suspects: They looked at 527 children who might have had meningitis.
• The Confirmed Cases: After running lab tests (like checking the fingerprints of the bacteria), they confirmed 69 children definitely had it. Another 120 had strong signs of it but couldn't prove exactly which bacteria was there (these are called "probable" cases).

2. Who Got Hit the Hardest?

Just like a storm hits the youngest saplings the hardest, this infection hit the babies and toddlers the most.

• Almost 8 out of 10 of the confirmed cases were children under 2 years old.
• The most common symptoms were like a severe flu on steroids: high fever, looking very sleepy or confused, and having seizures (shaking fits).

3. The "Big Three" Hackers

The doctors identified the specific bacteria causing the trouble. It wasn't a random mix; it was mostly three main villains:

• The Pneumococcus (S. pneumoniae): The most common culprit (about 26% of cases).
  • The Twist: The hospital uses a vaccine (PCV10) that covers 10 specific "versions" of this bacteria. But the bacteria are smart! They are evolving. The study found that the strains causing meningitis were mostly new versions that the current vaccine doesn't cover yet. It's like the hackers changed their passwords, and the old security software didn't recognize them.
• The Hib (Haemophilus influenzae): The second most common (about 17%).
  • The Good News: There is a vaccine for this. Most of these cases were the "Type B" version, which the vaccine is designed to stop. However, some kids who had the vaccine still got sick. This suggests the vaccine might need a "booster shot" (an extra dose) to keep the protection strong as kids get older.
• The Meningococcus (N. meningitidis): The third villain (about 10%).
  • The Situation: Colombia doesn't give this vaccine to every baby yet (it's mostly for high-risk groups). The study found that the "Group C" version was the most common here.

4. The Cost of the Attack

Meningitis is expensive, both in money and in human life.

• The Toll: Sadly, 11.6% of the children with confirmed meningitis died. That's roughly 1 in 9.
• The Aftermath: Of the children who survived, 26% were left with permanent scars on their "computer," such as hearing loss or brain damage.
• The Hospital Stay: Kids with confirmed meningitis stayed in the hospital for an average of 24.5 days—a long time to be away from home and family.

5. The "Security Software" (Vaccines)

The study showed that the vaccines are doing some work, but the bacteria are playing a game of "whack-a-mole."

• Because of the vaccines, the old, common versions of the bacteria are disappearing.
• However, the bacteria are "replacing" themselves with new, unvaccinated versions. This is called serotype replacement.
• The doctors are saying: "We need to update our security software (vaccines) to cover these new versions, or we need a universal shield that covers all versions."

The Bottom Line

This paper is a warning and a guide. It tells us that while we have made progress with vaccines, the bacteria are evolving. The "Sentinel" system (the watchtower) is crucial because it spots these changes early.

The main takeaway for parents and policymakers:

1. Keep vaccinating: It's still the best defense we have.
2. Watch the babies: They are the most vulnerable.
3. Update the plan: We might need new vaccines that cover the "new" versions of the bacteria, or we might need to give extra booster shots to keep the protection strong.

In short, the war against bacterial meningitis is ongoing. The doctors in Colombia are keeping a sharp eye on the battlefield to make sure the next generation of vaccines is ready to stop the hackers before they crash the system.

Technical Summary

1. Problem Statement

Bacterial meningitis (BM) remains a critical global public health challenge, particularly in children under five years of age. While conjugate vaccines have reduced the incidence of specific pathogens (e.g., Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis), the disease burden persists due to:

• Serotype Replacement: The emergence of non-vaccine serotypes following the introduction of vaccines (e.g., PCV10).
• Antimicrobial Resistance: The development of strains with reduced susceptibility to standard treatments.
• High Morbidity and Mortality: In low-to-middle-income settings, mortality can reach 54%, with up to 24% of survivors suffering chronic neurological sequelae.
• Data Gaps: There is a need for localized, high-quality epidemiological data to evaluate the impact of national immunization programs and guide public health policy in Colombia.

2. Methodology

• Study Design: A descriptive, cross-sectional study conducted at HOMI (Fundación Hospital Pediátrico la Misericordia), a tertiary-level pediatric hospital in Bogotá, Colombia.
• Period: January 1, 2016, to December 31, 2023.
• Population: Children under 5 years of age hospitalized with a clinical diagnosis of suspected bacterial meningitis.
• Case Definitions:
  • Suspected: Clinical diagnosis of meningitis requiring hospitalization.
  • Probable: CSF cytochemical analysis showing turbidity, leukocytes >100/mm³, protein >100 mg/dL, glucose <40 mg/dL, or Gram stain positive with negative culture.
  • Confirmed: Positive culture (blood or CSF) via Vitek 2 or positive molecular testing (FilmArray/PCR) for bacterial pathogens.
• Laboratory Procedures:
  • Identification: Vitek 2 system for bacterial identification.
  • Serotyping/Serogrouping: Quellung reaction or slide agglutination for S. pneumoniae, H. influenzae, and N. meningitidis.
  • Molecular Testing: Real-time PCR and multiplex PCR (since 2018) for genes lytA, hpd, sodC/ctrA to identify pathogens and serotypes in culture-negative cases.
  • Antimicrobial Susceptibility: Disk diffusion and broth microdilution against a panel of 10 antibiotics (e.g., penicillin, ceftriaxone, vancomycin).
• Data Analysis: Descriptive statistics for demographics, clinical presentation, incidence rates, mortality, and sequelae.

3. Key Contributions

• Sentinel Surveillance Validation: Demonstrates the efficacy of a multi-institutional sentinel surveillance network (involving the National Institute of Health, Ministry of Health, and PAHO/WHO) in capturing high-quality data during a period that included the COVID-19 pandemic.
• Etiological Shift Analysis: Provides detailed evidence of the shift in S. pneumoniae serotypes in Colombia post-PCV10 introduction, highlighting the dominance of non-vaccine serotypes.
• Vaccine Impact Assessment: Evaluates the real-world effectiveness of the Hib and PCV10 vaccines, noting cases of vaccine failure and the persistence of serotype b (Hib) despite vaccination.
• Molecular Integration: Successfully integrated molecular diagnostics (PCR) to identify pathogens in culture-negative cases, increasing the confirmed case detection rate compared to culture alone.

4. Key Results

• Case Distribution:
  • Total Suspected: 527 cases.
  • Probable Cases: 120 (22.8%).
  • Confirmed Cases: 69 (13.1%).
  • Peak Year: 2019 had the highest incidence (1.87 per 1,000 hospitalized children <5 years).
• Demographics:
  • Age: 78.2% of confirmed cases were children under 2 years old.
  • Sex: Slight male predominance (59.4%).
• Clinical Presentation:
  • Symptoms: Fever (98.3%), altered consciousness (39.1%), seizures (36.2%), and lethargy (27.5%).
  • Outcomes: Mortality rate was 11.6% (8/69). Among survivors, 26.1% developed sequelae.
  • Hospital Stay: Median stay for confirmed cases was 24.5 days (vs. 10 days for probable cases).
• Etiology (Confirmed Cases):
  • Streptococcus pneumoniae: 26.1% (Most common). All viable isolates were non-PCV10 serotypes (e.g., 19A, 23B, 15C, 6C/6D).
  • Escherichia coli: 21.7% (Notable for occurring outside the neonatal period).
  • Haemophilus influenzae: 17.4%. Of these, 77.7% were serotype b (Hib), occurring in both vaccinated and unvaccinated children.
  • Neisseria meningitidis: 10.1%. 60% were Serogroup C, 40% Serogroup Y.
  • Other: S. agalactiae, K. pneumoniae, L. monocytogenes, etc.
• Antimicrobial Resistance: Most isolates were pansensitive. However, some S. pneumoniae showed resistance to Erythromycin and SXT; some H. influenzae showed resistance to Ampicillin and SXT.
• Vaccination Status:
  • 57.7% of confirmed S. pneumoniae cases had received PCV10.
  • 73.3% of confirmed H. influenzae cases had received Hib vaccine.
  • No patients had received meningococcal vaccines (not part of the national schedule).

5. Significance and Conclusion

• Public Health Policy: The study confirms that while PCV10 has successfully reduced vaccine-type pneumococcal disease, serotype replacement is a significant ongoing threat. This supports the discussion for transitioning to broader-coverage vaccines (e.g., PCV13 or PCV15/20) or developing universal protein-based vaccines.
• Hib Re-emergence: The persistence of Hib meningitis in vaccinated children suggests potential issues with vaccine schedules, antibody waning, or strain virulence, supporting the 2023 Colombian policy change to include a Hib booster at 18 months.
• Meningococcal Gap: The presence of Serogroup C and Y highlights the need for cost-effectiveness analyses regarding the introduction of universal Men-ACWY vaccination in Colombia.
• Surveillance Value: The study underscores that active, laboratory-based sentinel surveillance is essential for monitoring disease dynamics, detecting outbreaks, and evaluating the long-term impact of immunization programs in resource-limited settings.

Limitations: The study is single-center (tertiary hospital), which may introduce selection bias toward more severe cases, limiting generalizability to the entire Colombian population. Additionally, not all isolates could be recovered for phenotypic characterization.