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Invasive Pneumococcal Disease Prevention in Adults

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Invasive Pneumococcal Disease in Alaskan Adults Experiencing Homelessness

—Low uptake of pneumococcal conjugate vaccines among adults contributes to an increase in invasive pneumococcal disease, especially in those experiencing homelessness, say the Alaska-based authors of a new study.

By Deborah L. Ungerleider, MD, FAAP
Reviewed by Joseph Yabes, MD

Invasive pneumococcal disease (IPD) can be dangerous to people at any age, but those most at increased risk for IPD are adults ≥65 years of age, people with certain underlying medical conditions, and individuals experiencing homelessness. Yet despite the availability of pneumococcal conjugate vaccines (PCVs) for both children and adults, which can decrease the incidence of IPD, there are still cases that could have been prevented with higher uptake of the newest PCVs, PCV15 and PCV20.1

Keeping this in mind, the investigators of a new study, from the Arctic Investigations Program (AIP), Centers for Disease Control and Prevention (CDC), Anchorage, Alaska, evaluated the epidemiology of IPD cases reported among adults and persons experiencing homelessness in Alaska over a 10-year period, from 2011 through 2020.1 The researchers compared the incidence of IPD, looked for trends over time, and then estimated the number of cases that were potentially preventable if people had been vaccinated with PCV15 or PCV20.

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For their analysis, the authors defined IPD as infection with Streptococcus pneumoniae in blood or cerebrospinal fluid. Serotyping of the specimens was done by the CDC AIP. Pneumococcal vaccination was defined as receipt of ≥1 dose of PCV by an individual before a positive culture or nucleic acid amplification test.

Which groups were the most vulnerable?

During the study period, the average annual incidence of IPD among Alaskan adults (n=1164) was 21.3 per 100,000 persons, a rate that increased over the study period (P<.01).1 The authors stated that this was largely due to higher amounts of IPD caused by serotypes 4 and 12F. Males and older adults in particular had higher rates of IPD. For males, the annual incidence was 25 per 100,000, versus 18 per 100,000 for females. In terms of age, the rates were 41 per 100,000, 28 per 100,000, and 8 per 100,000 for those ≥65 years old, 40 to 64 years old, and 18 to 39 years old, respectively. In addition, Native Alaskan individuals had a 4.7 times higher incidence of IPD (95% confidence interval 4.2 to 5.2) than non-Native Alaskans.

For adults experiencing homelessness in Anchorage, the average annual incidence of IPD during the study period was 1186 per 100,000, compared to 19 per 100,000 in the general adult population. The adults experiencing homelessness were younger and more likely to be a Native Alaskan. While they were less likely to have had a PCV dose, they were more likely than the general public with IPD to have an underlying medical condition but less likely to die.

The clinical syndromes comprising the IPD cases were as follows:

  • Pneumonia (78%)
  • Bacteremia without a focus (13%)
  • Meningitis (4%)
  • Empyema (4%)

Other demographics of the study population included:

  • ≥1 underlying medical condition (85%)
  • Had received ≥1 dose of PCV (8%)
  • Hospitalized (90%)
  • Deaths (13%)

Rates of PCV vaccination

Majority of the patients (89%) who had IPD were eligible for a PCV vaccine. Of those, 27% were ≥65 years old and 62% were 19 to 64 years old with ≥1 underlying medical condition (smoking, alcohol abuse, diabetes, chronic lung disease, cancer).

Serotyping revealed 5 S pneumoniae serotypes comprising 41% of all IPD cases, with the breakdown as follows: 

  • 12F (10%), contained in PCV20
  • 4 (9%), contained in PCV13, PCV15, and PCV20 
  • 3 (9%), contained in PCV13
  • 22F (7%), contained in PCV15
  • 8 (7%), contained in PCV20

Of the adults with IPD who were experiencing homelessness, 94% were eligible for PCV, with 4% being ≥65 years of age and 89% being between the ages of 19 and 64 with at least 1 underlying medical condition (alcohol abuse, smoking, congestive heart failure, and chronic lung disease). However, only 8% of individuals with IPD had received 1 or more doses of PCV. The breakdown of serotypes covered by a PCV for this cohort was: 32% (covered by PCV13 plus 6C), 37% (PCV15), and 68% (PCV20).

Limitations and conclusions

Although the current analysis made clear the disparities among Native Alaskans with IPD, the investigators pointed out several limitations to their study. For one, some years saw very few cases of IPD overall and among certain subgroups, which made it difficult to distinguish between annual trends and random variation.

In addition, some adults may not have been classified properly, as classification was based on medical record reviews done during periods of homelessness. This “point in time” approach likely underestimated the number of homeless adults, which could have led to a higher estimation of IPD in this population. Additionally, this study included adults experiencing homelessness in Anchorage only and therefore may not represent IPD in other places.

Another possible limitation is that the indications for pneumococcal vaccination by the CDC’s Advisory Committee on Immunization Practices are slightly different from the underlying conditions and risk factors used in this study from Alaskan surveillance records.

Finally, in an interview with ѿapp, first author Jonathan Steinberg, RN, MPH, a member of the Arctic Investigations Program, Centers for Disease Control and Prevention in Anchorage, summarized his team’s hope for the future use of PCVs: “New PCVs that protect against an increased number of S pneumoniae serotypes, coupled with updated vaccination guidelines, have the potential to reduce the burden of IPD among adults, including adults experiencing homelessness.”

Published:

Deborah Ungerleider is a New Jersey-based pediatrician and freelance medical writer and editor who covers numerous aspects of medical practice.

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