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. 2024 Jun 7;24(1):568.
doi: 10.1186/s12879-024-09425-7.

Syndromic case definitions for lower respiratory tract infection (LRTI) are less sensitive in older age: an analysis of symptoms among hospitalised adults

Rachel Kwiatkowska  1   2 , Anastasia Chatzilena  3 , Jade King  4 , Madeleine Clout  5 , Serena McGuinness  5 , Nick Maskell  6 , Jennifer Oliver  5 , Robert Challen  3 , Matthew Hickman  1   2 , Adam Finn  1   2   5   7 , Catherine Hyams  1   4   5   8 , Leon Danon  9   10 ; AvonCAP Research Group
Collaborators, Affiliations

Syndromic case definitions for lower respiratory tract infection (LRTI) are less sensitive in older age: an analysis of symptoms among hospitalised adults

Rachel Kwiatkowska et al. BMC Infect Dis. .

Abstract

Background: Lower Respiratory Tract Infections (LRTI) pose a serious threat to older adults but may be underdiagnosed due to atypical presentations. Here we assess LRTI symptom profiles and syndromic (symptom-based) case ascertainment in older (≥ 65y) as compared to younger adults (< 65y).

Methods: We included adults (≥ 18y) with confirmed LRTI admitted to two acute care Trusts in Bristol, UK from 1st August 2020- 31st July 2022. Logistic regression was used to assess whether age ≥ 65y reduced the probability of meeting syndromic LRTI case definitions, using patients' symptoms at admission. We also calculated relative symptom frequencies (log-odds ratios) and evaluated how symptoms were clustered across different age groups.

Results: Of 17,620 clinically confirmed LRTI cases, 8,487 (48.1%) had symptoms meeting the case definition. Compared to those not meeting the definition these cases were younger, had less severe illness and were less likely to have received a SARS-CoV-2 vaccination or to have active SARS-CoV-2 infection. Prevalence of dementia/cognitive impairment and levels of comorbidity were lower in this group. After controlling for sex, dementia and comorbidities, age ≥ 65y significantly reduced the probability of meeting the case definition (aOR = 0.67, 95% CI:0.63-0.71). Cases aged ≥ 65y were less likely to present with fever and LRTI-specific symptoms (e.g., pleurisy, sputum) than younger cases, and those aged ≥ 85y were characterised by lack of cough but frequent confusion and falls.

Conclusions: LRTI symptom profiles changed considerably with age in this hospitalised cohort. Standard screening protocols may fail to detect older and frailer cases of LRTI based on their symptoms.

Keywords: Age factors; Missed diagnosis; Pneumonia; Public health surveillance; Respiratory tract infections.

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Conflict of interest statement

CH is Principal Investigator of the AvonCAP study, a University of Bristol sponsored study which is funded by Pfizer. JO is a Co-Investigator on the AvonCAP Study. AF is a member of the UK Dept of Health, Joint Committee on Vaccination and Immunization (JCVI) and, until December 2022, was chair of the World Health Organization European Technical Advisory Group of Experts on Immunization (ETAGE). In addition to receiving funding for this study from Pfizer as Chief Investigator, he leads another project investigating transmission of respiratory bacteria in families jointly funded by Pfizer and the Gates Foundation and is chief or principal investigator in current or recent COVID-19 vaccine trials funded by Astra-Zeneca, Valneva and Sanofi. LD, RC are also partly funded through AvonCAP. LD is a Co-Investigator of the AvonCAP study and has also received funding from Pfizer, UKRI and UKHSA for unrelated projects. RK holds an honorary contract with the UK Health Security Agency (UKHSA). The corresponding author had full access to all data in the study and final responsibility for the decision to submit for publication. All the other authors do not have any competing interests.

Figures

Fig. 1
Fig. 1
Age distribution of LRTI cases. The age distribution of LRTI cases by SARS-CoV-2 status and whether patients presented with symptom profiles consistent with the LRTI case definition. A Counts of cases per quarter, by year of age, with dotted lines showing counts of SARS-CoV-2 LRTI and solid lines showing counts of other LRTI; B Age distribution of SARS-CoV-2 negative cases and C SARS-CoV-2 positive cases. Each row represents a quarter (Q) from Q3 2020 through to Q3 2022, except for the first and last rows which are truncated due to the time period of this analysis
Fig. 2
Fig. 2
Age-specific symptom profiling for LRTI. A Comparison of LRTI symptom expression in older (≥ 65y) vs. younger (< 65y) adults is shown as a probability of each symptom occurring, with weighted log-odds ratios expressed as z-scores (number of standard deviations from the mean). B Cases are grouped in 10y age bands (rows), and cells are coloured based on frequency of a symptom within each age band relative to all other symptoms within the age band. Frequencies are presented as z-scores. C Age bands are assigned to clusters based on similarity of LRTI symptom profiles (Principal Components) and plotted according to PC1 and PC2 scores
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