Geographic Prevalence of Streptococcus pneumoniae Serotype 4
Serotype 4 is highly prevalent in the western United States, particularly in Alaska, Colorado, the Navajo Nation, New Mexico, and Oregon, where it causes ≥30% of invasive pneumococcal disease (IPD) cases. 1
Regional Distribution Patterns
High-Prevalence Regions (Western United States)
Based on CDC Active Bacterial Core surveillance data, serotype 4 demonstrates striking geographic concentration:
- Alaska: Documented high percentages of serotype 4 IPD 1
- Navajo Nation: Significant burden with ≥30% of IPD cases 1
- Colorado, New Mexico, Oregon: Confirmed high prevalence through surveillance 1
- Other western states: Prevalence unknown due to lack of IPD surveillance systems 1
Low-Prevalence Regions
Midwestern, eastern, and southern United States show minimal serotype 4 activity, with no significant percentages detected through surveillance 1. When serotype 4 IPD does occur in these regions, it typically affects:
- Adults aged <65 years
- Persons with specific risk factors: alcoholism, chronic lung disease, cigarette smoking, homelessness, injection drug use
- Individuals who have not received serotype 4-containing vaccines 1
International Context
Canada
Alberta, Canada experienced a serotype 4 outbreak, particularly in Calgary among persons experiencing homelessness or using illicit drugs 2. Whole-genome sequencing identified an emergent ST244 lineage primarily associated within Alberta, with nationally distributed clades ST205 and ST695.
Northern Europe
Shipyard outbreaks of serotype 4 ST801 occurred in Norway, Finland, and Northern Ireland 3. Genomic analysis revealed near-identical strains (0-2 SNPs) between Norwegian and Finnish outbreaks, suggesting international transmission between shipyards around 2017.
Switzerland
Serotype 4 was among the most frequent serotypes (along with 1,3, 6B, 7F, 14, 19F, and 23F) and demonstrated increased invasive potential compared to colonizing isolates 4.
Clinical Implications for Vaccine Selection
In western U.S. regions with high serotype 4 prevalence, avoid PCV21 as it does not contain serotype 4. Instead, use PCV20 alone or PCV15 plus PPSV23 to ensure serotype 4 coverage 5, 1. This is critical because serotype 4 accounts for a substantial proportion of preventable IPD in these areas.
For other U.S. regions where serotype 4 is uncommon, PCV21 may be appropriate as it provides coverage against eight unique serotypes not found in other vaccines 1.
Important Caveats
- Serotype 4 IPD significantly declined after PCV7 introduction in children but has recently reemerged in certain regions 1
- The reemergence appears linked to vulnerable populations: homeless individuals, substance users, and those with chronic conditions 2
- Harsh environmental and living conditions (e.g., shipyards, homelessness) may facilitate invasion of colonizing pneumococci 3
- Geographic surveillance data outside the western U.S. remains incomplete, making prevalence estimates uncertain in many areas 1