---
title: "All-cause pneumonia and influenza hospitalizations by coding position in US claims, 2014–2023"
id: "pubmed-42830285"
canonical_url: "https://medichelpline.com/clinical-feed/pubmed-42830285"
content_type: "clinical_feed_article"
specialty: "Critical Care"
source_name: "PubMed / NCBI"
source_url: "https://pubmed.ncbi.nlm.nih.gov/42830285/"
doi: "10.1186/s41479-026-00207-0"
published_at: "2026-10-05T00:00:00.000Z"
evidence_level: "Journal Article"
license: "CC-BY-NC-4.0 / Informational Use"
---
# All-cause pneumonia and influenza hospitalizations by coding position in US claims, 2014–2023
## Provenance & Clinical Metadata
- **Canonical URL:** https://medichelpline.com/clinical-feed/pubmed-42830285
- **Specialty:** [Critical Care](https://medichelpline.com/clinical-feed/critical-care.md)
- **Primary Source:** PubMed / NCBI
- **Source URL:** [Original Journal Publication](https://pubmed.ncbi.nlm.nih.gov/42830285/)
- **DOI:** [10.1186/s41479-026-00207-0](https://doi.org/10.1186%2Fs41479-026-00207-0)
- **Published At:** 2026-10-05T00:00:00.000Z
- **Evidence Rating:** Journal Article
## Executive GIST (TL;DR)
- The study examined trends in **all-cause pneumonia and influenza (ACPI)** inpatient hospitalizations among US adults using healthcare claims from 2014–2023. - Authors evaluated two case definitions: a strict **principal ACPI** definition (principal diagnosis field only) and an **expanded principal ACPI** definition that included hospitalizations with principal codes for sepsis, meningitis, COPD, empyema, or acute respiratory failure when ACPI appeared as a secondary code. - The incidence based on the **principal ACPI** definition showed the largest decline over the study period, with declines most pronounced in younger adult age groups compared with older adults. - The expanded principal ACPI definition captured a substantially larger share of ACPI events present in any diagnostic field (between **48.5% and 63.4%**) and exhibited less variation over time than the principal-only definition. - Using only principal diagnostic codes would exclude roughly **30%** of hospitalizations that met the expanded principal ACPI definition, potentially exaggerating the apparent decline in ACPI hospitalizations. - There was a documented shift toward greater use of **sepsis** and **COPD** codes in the principal diagnostic position over the study period, which may reflect coding practice changes. - Prevalence of risk factors associated with pneumococcal pneumonia, influenza, or RSV increased across the study period, particularly between 2020 and 2023; in 2023, more than **96%** of adults ≥65 years hospitalized with ACPI had at least one such risk factor in the prior three years. - The study used secondary, non-identifiable claims data; ethical approval and consent for publication were not required. Several authors are employees of Merck & Co., Inc., disclosed as competing interests. - The findings imply that outcome definitions based solely on principal diagnostic codes can underestimate or mischaracterize hospitalizations for respiratory infections and that coding shifts during the pandemic period may influence administrative-data estimates.
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Affiliations Expand ### Affiliations * 1 Merck & Co., Inc, Rahway, NJ, USA. kelsie.cassell@merck.com. * 2 Merck & Co., Inc, Rahway, NJ, USA. * PMID: **42830285** * DOI: [ 10.1186/s41479-026-00207-0 ](https://doi.org/10.1186/s41479-026-00207-0) Item in Clipboard # Trends in all-cause pneumonia and influenza hospitalization incidence by coding position - a study of US healthcare claims, 2014-2023 Kelsie Cassell et al. Pneumonia (Nathan). 2026. Show details Display options Display options Format Abstract PubMed PMID Pneumonia (Nathan) Actions * [ Search in PubMed ](https://pubmed.ncbi.nlm.nih.gov/?term=%22Pneumonia+%28Nathan%29%22%5Bjour%5D&sort=date&sort_order=desc) * [ Search in NLM Catalog ](https://www.ncbi.nlm.nih.gov/nlmcatalog?term=%22Pneumonia+%28Nathan%29%22%5BTitle+Abbreviation%5D) * [ Add to Search ](https://pubmed.ncbi.nlm.nih.gov/42830285/) . 2026 Oct 5;18(1):22. doi: 10.1186/s41479-026-00207-0. ### Authors [Kelsie Cassell](https://pubmed.ncbi.nlm.nih.gov/?term=Cassell+K&cauthor_id=42830285)[ 1 ](https://pubmed.ncbi.nlm.nih.gov/42830285/#short-view-affiliation-1 "Merck & Co., Inc, Rahway, NJ, USA. kelsie.cassell@merck.com."), [Salini Mohanty](https://pubmed.ncbi.nlm.nih.gov/?term=Mohanty+S&cauthor_id=42830285)[ 2 ](https://pubmed.ncbi.nlm.nih.gov/42830285/#short-view-affiliation-2 "Merck & Co., Inc, Rahway, NJ, USA."), [Kelly D Johnson](https://pubmed.ncbi.nlm.nih.gov/?term=Johnson+KD&cauthor_id=42830285)[ 2 ](https://pubmed.ncbi.nlm.nih.gov/42830285/#short-view-affiliation-2 "Merck & Co., Inc, Rahway, NJ, USA."), [Thomas Weiss](https://pubmed.ncbi.nlm.nih.gov/?term=Weiss+T&cauthor_id=42830285)[ 2 ](https://pubmed.ncbi.nlm.nih.gov/42830285/#short-view-affiliation-2 "Merck & Co., Inc, Rahway, NJ, USA."), [Nicole Cossrow](https://pubmed.ncbi.nlm.nih.gov/?term=Cossrow+N&cauthor_id=42830285)[ 2 ](https://pubmed.ncbi.nlm.nih.gov/42830285/#short-view-affiliation-2 "Merck & Co., Inc, Rahway, NJ, USA.") ### Affiliations * 1 Merck & Co., Inc, Rahway, NJ, USA. kelsie.cassell@merck.com. * 2 Merck & Co., Inc, Rahway, NJ, USA. * PMID: **42830285** * DOI: [ 10.1186/s41479-026-00207-0 ](https://doi.org/10.1186/s41479-026-00207-0) Item in Clipboard Cite Display options Display options Format Abstract PubMed PMID Linked Discoveries ## Abstract **Background:** The hospitalization rate for pneumonia among adults has decreased in the U.S. since the early 2000's. The increasing prevalence of chronic conditions among adults, especially those associated with risk factors for pneumonia caused by Streptococcus pneumoniae, influenza and respiratory syncytial virus, may be contributing to a larger population susceptible to pneumonia. Existing estimates utilizing claims data may underestimate the true rates of disease due to how diagnostic coding fields are used to define outcomes. **Methods:** A retrospective descriptive study of adult (> 18 years) ACPI inpatient hospitalizations was conducted using US healthcare claims data from 2014 to 2023. Principal ACPI hospitalizations were defined as those with a principal field code for ACPI only. Expanded principal ACPI hospitalizations were those with a principal code for ACPI or a principal code for sepsis, meningitis, COPD, empyema, and acute respiratory failure in combination with a secondary code for ACPI. Prevalence of risk factors indicative for pneumococcal pneumonia, RSV, or severe influenza vaccination were assessed. **Results:** Principal ACPI showed the largest decline in incidence and this decline was greatest among the younger age groups compared to the older adults. In contrast, the expanded principal definition of ACPI captured between 48.5 and 63.4% of ACPI codes present in any field and showed lower variation over time compared to the principal definition. The proportion of adults with a risk factor of interest increased during the study period, particularly between 2020 and 2023. Greater than 96% of adults ≥ 65y hospitalized with ACPI in 2023 had at least one risk factor indicative for vaccination against pneumococcal, influenza, or RSV in the 3 years prior. **Conclusions:** We show that using only principal diagnostic codes to identify ACPI hospitalization may disproportionately inflate the decline in ACPI hospitalizations between 2014 and 2023. Using a principal ACPI hospitalization definition would exclude approximately 30% of hospitalizations that would meet the expanded principal ACPI definition. The shift towards greater use of sepsis and COPD codes in the principal diagnostic code position may be attributed to coding changes over the study period. Risk factors for pneumonia increased in prevalence, particularly during the COVID-19 pandemic period. **Keywords:** All-cause pneumonia; Claims; Comorbidities; Diagnostic codes; Influenza. © 2026. Merck & Co., Inc., Rahway, NJ, USA and its affiliates. [PubMed Disclaimer](https://pubmed.ncbi.nlm.nih.gov/disclaimer/) ## Conflict of interest statement Declarations. Ethical approval: Ethical approval was not required as part of this study of secondary, non-identifiable healthcare claims data. Consent for publication: Consent for publication was not necessary for this study. Competing interests: Kelsie Cassell, Salini Mohanty, Kelly Johnson, and Nicole Cossrow are employees of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA who may own stock/or hold stock options in Merck & Co., Inc., Rahway, NJ, USA. ## References 1. 1. Salah HM, Minhas AMK, Khan MS, Pandey A, Michos ED, Mentz RJ, et al. Causes of hospitalization in the USA between 2005 and 2018. Eur Heart J Open. 2021;1(1):oeab001. . PubMed PMID: 35919090; PubMed Central PMCID: PMC9242058. - [DOI](https://doi.org/10.1093/ehjopen/oeab001) - [PubMed](https://pubmed.ncbi.nlm.nih.gov/35919090/) - [PMC](https://pmc.ncbi.nlm.nih.gov/articles/9242058/) 2. 1. Griffin MR, Zhu Y, Moore MR, Whitney CG, Grijalva CG. U.S. hospitalizations for pneumonia after a decade of pneumococcal vaccination. N Engl J Med. 2013;369(2):155–63. . PubMed PMID: 23841730; PubMed Central PMCID: PMC4877190. - [DOI](https://doi.org/10.1056/nejmoa1209165) - [PubMed](https://pubmed.ncbi.nlm.nih.gov/23841730/) - [PMC](https://pmc.ncbi.nlm.nih.gov/articles/4877190/) 3. 1. Advisory Committee on Immunization Practices. Preventing pneumococcal disease among infants and young children. Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2000;49(RR–9):1–35. PubMed PMID: 11055835. 4. 1. Fiore AE, Uyeki TM, Broder K, Finelli L, Euler GL, Singleton JA, et al. Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2010. MMWR Recomm Rep. 2010;59(RR–8):1–62. PubMed PMID: 20689501. - [PubMed](https://pubmed.ncbi.nlm.nih.gov/20689501/) 5. 1. Musher DM, Anderson R, Feldman C. The remarkable history of pneumococcal vaccination: an ongoing challenge. Pneumonia (Nathan). 2022;14:5. . 00097-y PubMed PMID: 36153636; PubMed Central PMCID: PMC9509586. - [DOI](https://doi.org/10.1186/s41479-022) - [PubMed](https://pubmed.ncbi.nlm.nih.gov/36153636/) - [PMC](https://pmc.ncbi.nlm.nih.gov/articles/9509586/) Show all 52 references [x] Cite Copy Download .nbib .nbib Format: AMA APA MLA NLM **Send To** * [Clipboard](https://pubmed.ncbi.nlm.nih.gov/42830285/) * [Email](https://account.ncbi.nlm.nih.gov/?back_url=https%3A%2F%2Fpubmed.ncbi.nlm.nih.gov%2F42830285%2F%23open-email-panel) * [Save](https://pubmed.ncbi.nlm.nih.gov/42830285/) * [My Bibliography](https://account.ncbi.nlm.nih.gov/?back_url=https%3A%2F%2Fpubmed.ncbi.nlm.nih.gov%2F42830285%2F%23open-bibliography-panel) * [Collections](https://account.ncbi.nlm.nih.gov/?back_url=https%3A%2F%2Fpubmed.ncbi.nlm.nih.gov%2F42830285%2F%23open-collections-panel) * [Citation Manager](https://pubmed.ncbi.nlm.nih.gov/42830285/) [x] NCBI Literature Resources [MeSH](https://www.ncbi.nlm.nih.gov/mesh/) [PMC](https://www.ncbi.nlm.nih.gov/pmc/) [Bookshelf](https://www.ncbi.nlm.nih.gov/books) [Disclaimer](https://pubmed.ncbi.nlm.nih.gov/disclaimer/) The PubMed wordmark and PubMed logo are registered trademarks of the U.S. Department of Health and Human Services (HHS). 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