Trends in invasive and non-invasive Streptococcus pneumoniae disease in adults hospitalised in Bristol and Bath: a retrospective cohort study, 2006–2022

Background:

Pneumococcal surveillance typically focuses on cases identified by positive microbiology and collects limited clinical data. The majority of pneumococcal studies in the literature focus on invasive respiratory disease. This study includes a cohort of all cause pneumococcal disease, including non-invasive disease and non-respiratory invasive disease with detailed clinical outcomes, allowing a more complete view of pneumococcal disease burden, and particularly meningitis cases.

Methods:

A longitudinal adult cohort of invasive and non-invasive pneumococcal disease inpatients in three hospitals between 2006 and 2022, was retrospectively collected. The demographics and outcomes of invasive and non-invasive hospitalised cases were compared. Features of invasive disease in different clinical presentations, particularly meningitis, were compared to invasive respiratory disease. Serotype distributions of different presentations in invasive disease were compared using bootstrap resampling.

Results:

Out of a total 3719 all cause pneumococcal disease, 1419 cases (38.2%) were invasive respiratory disease. Non-invasive disease was seen in 2033 cases (54.7%). Non-invasive disease had a lower (but clinically substantial) 30 day case-fatality rate than invasive disease (11.7% versus 14.8%; P = 0.005), and similar lengths of stay in hospital. Among the 1686 invasive cases, 258 (15.3%) were outside the respiratory tract. The 172 cases presenting with meningitis were younger (54.9y vs. 66.8y; P < 0.001) than those with lower respiratory tract infection; and had high rates of intensive care admission (63.4% vs. LRTI 10.2%; P < 0.001). We found no evidence of a different serotype distribution between different clinical presentations.

Conclusions:

There is a substantial burden of pneumococcal disease that is not represented by studies that focus on invasive respiratory disease, or by surveillance that focus only on culture positive disease alone. Outcomes are particularly poor in the case of meningitis, but non-invasive disease also has a high case fatality rate. Given the same serotypes are found in meningitis as invasive respiratory disease, we anticipate that the same vaccines that target respiratory disease should be relevant to the prevention of meningitis.