Recurrent pneumococcal invasive disease in the region of Madrid during a five-year period

Prior exposure to pathogens augments host heterogeneity in susceptibility and has key epidemiological consequences

Pathogen epidemics are key threats to human and wildlife health. Across systems, host protection from pathogens following initial exposure is often incomplete, resulting in recurrent epidemics through partially-immune hosts. Variation in population-level protection has important consequences for epidemic dynamics, but how acquired protection influences inter-individual heterogeneity in susceptibility and its epidemiological consequences remains understudied. We experimentally investigated whether prior exposure (none, low-dose, or high-dose) to a bacterial pathogen alters host heterogeneity in susceptibility among songbirds. Hosts with no prior pathogen exposure had little variation in protection, but heterogeneity in susceptibility was significantly augmented by prior pathogen exposure, with the highest variability detected in hosts given high-dose prior exposure. An epidemiological model parameterized with experimental data found that heterogeneity in susceptibility from prior exposure more than halved epidemic sizes compared with a homogeneous population with identical mean protection. However, because infection-induced mortality was also greatly reduced in hosts with prior pathogen exposure, reductions in epidemic size were smaller than expected in hosts with prior exposure. These results highlight the importance of variable protection from prior exposure and/or vaccination in driving population-level heterogeneity and epidemiological dynamics.

Prior exposure to pathogens augments host heterogeneity in susceptibility and has key epidemiological consequences

Pathogen epidemics are key threats to human and wildlife health. Across systems, host protection from pathogens following initial exposure is often incomplete, resulting in recurrent epidemics through partially-immune hosts. Variation in population-level protection has important consequences for epidemic dynamics, but how acquired protection influences inter-individual heterogeneity in susceptibility and its epidemiological consequences remains understudied. We experimentally investigated whether prior exposure (none, low-dose, or high-dose) to a bacterial pathogen alters host heterogeneity in susceptibility among songbirds. Hosts with no prior pathogen exposure had little variation in protection, but heterogeneity in susceptibility was significantly augmented by prior pathogen exposure, with the highest variability detected in hosts given high-dose prior exposure. An epidemiological model parameterized with experimental data found that heterogeneity in susceptibility from prior exposure more than halved epidemic sizes compared with a homogeneous population with identical mean protection. However, because infection-induced mortality was also greatly reduced in hosts with prior pathogen exposure, reductions in epidemic size were smaller than expected in hosts with prior exposure. These results highlight the importance of variable protection from prior exposure and/or vaccination in driving population-level heterogeneity and epidemiological dynamics.

Clinical Presentations and Outcomes of Children in Canada With Recurrent Invasive Pneumococcal Disease From the IMPACT Surveillance Network

BACKGROUND

Invasive pneumococcal disease due to Streptococcus pneumoniae can cause mortality and severe morbidity due to sepsis, meningitis and pneumonia, particularly in young children and the elderly. Recurrent invasive pneumococcal disease is rare yet serious sequelae of invasive pneumococcal disease that is associated with the immunocompromised and leads to a high mortality rate.

METHOD

This retrospective study reviewed recurrent invasive pneumococcal disease cases from the Canadian Immunization Monitoring Program, ACTive (IMPACT) between 1991 and 2019, an active network for surveillance of vaccine-preventable diseases and adverse events following immunization for children ages 0-16 years. Data were collected from 12 pediatric tertiary care hospitals across all 3 eras of public pneumococcal conjugate vaccine implementation in Canada.

RESULTS

The survival rate within our cohort of 180 recurrent invasive pneumococcal disease cases was 98.3%. A decrease of 26.4% in recurrent invasive pneumococcal disease due to vaccine serotypes was observed with pneumococcal vaccine introduction. There was also a 69.0% increase in the rate of vaccination in children with preexisting medical conditions compared with their healthy peers.

CONCLUSION

The decrease in recurrent invasive pneumococcal disease due to vaccine-covered serotypes has been offset by an increase of non-vaccine serotypes in this sample of Canadian children.

Estimating the risk of recurrent invasive pneumococcal disease in Australia, 1991-2016

BACKGROUND

Individuals who experience an initial episode of invasive pneumococcal disease (IPD) are at increased risk of recurrent episodes. However, the magnitude of risk has not been well-quantified in the pneumococcal conjugate vaccine era. Individuals with a previous episode of IPD are not commonly identified as a high-risk group in vaccination guidelines.

METHODS

Australian residents with at least one case of IPD between 1991 and 2016 were identified using routine public health surveillance data which included identified IPD risk factors. Incidence of recurrent IPD was calculated from 2001 onwards (after IPD became nationally notifiable) using time-to-event analyses with individuals contributing person-time at risk of recurrence if they survived greater than 14 days after initial episode onset.

RESULTS

From 1991 to 2016 there were 28,809 IPD episodes in 28,218 individuals. A total of 512 (1.8%) persons experienced 591 recurrent episodes. From 2001 to 2016 the incidence of recurrent IPD was 216.2 per 100,000 person-years, 27 times greater than the population rate of primary IPD during this period (8.0 per 100,000 population per year). Between 2011 and 2016, more than one-quarter of individuals experiencing recurrence had no IPD risk factors identified at first episode.

CONCLUSIONS

There is substantially increased risk of recurrent IPD after an initial episode. At least one-quarter of those with recurrent episodes have no identified risk factors at the initial episode. Given the potential preventability of future episodes, those with a previous IPD episode should be identified as a high-risk group and receive pneumococcal vaccination.

Clinical and financial burden of hospitalised community-acquired pneumonia in patients with selected underlying comorbidities in England

Background

Hospitalised pneumonia may have long-term clinical and financial impact in adult patients with underlying comorbidities.

Methods

We conducted a retrospective cohort study using the Hospital Episode Statistics (HES) database to determine the clinical and financial burden over 3 years of hospitalised community-acquired pneumonia (CAP) to England’s National Health Service (NHS). Subjects were adults with six underlying comorbidities (chronic heart disease (CHD); chronic kidney disease (CKD); chronic liver disease (CLD); chronic respiratory disease (CRD); diabetes mellitus (DM) and post bone marrow transplant (post-BMT)) with an inpatient admission in 2012/2013. Patients with CAP in 2013/2014 were followed for 3 years and compared with similarly aged, propensity score-matched adults with the same comorbidity without CAP.

Findings

The RR of hospital admissions increased after CAP, ranging from 1.08 (95% CI 1.04 to 1.12) for CKD to 1.38 (95% CI 1.35 to 1.40) for CRD. This increase was maintained for at least 2 years. Mean difference in hospital healthcare costs (£) was higher for CAP patients in 2013/2014; ranging from £1115 for DM to £8444 for BMT, and remained higher for 4/6 groups for 2 more years, ranging from £1907 (95% CI £1573 to £2240) for DM to £11 167 (95% CI £10 847 to £11 486) for CRD.) The OR for mortality was significantly higher for at least 3 years after CAP, ranging from 4.76 (95% CI 4.12 to 5.51, p<0.0001) for CLD to 7.50 (95%CI 4.71 to 11.92, p<0.0001) for BMT.

Interpretation

For patients with selected underlying comorbidities, healthcare utilisation, costs and mortality increase for at least 3 years after being hospitalised CAP.

Pneumococcal conjugate vaccine failure in children: A systematic review of the literature

BACKGROUND

Pneumococcal conjugate vaccines (PCVs) are highly effective in preventing pneumococcal invasive disease (IPD) due to serotypes included in the vaccines. The risk of vaccine-type IPD in immunised children (i.e. vaccine failure) has not been systematically assessed in countries with established PCV programmes.

METHODS

We undertook a systematic review of the English literature published from January 2000 to April 2016 to evaluate the vaccine schedule, risk factors, serotype distribution, clinical presentation and outcomes of vaccine failure in children vaccinated with the 7-valent (PCV7), 10-valent (PCV10), and 13-valent (PCV13) vaccines. Data sources included MEDLINE, EMBASE, Cochrane library, and references within identified articles.

RESULTS

We identified 1742 potential studies and included 20 publications involving 7584 participants in children aged ⩽5year-olds: 5202 received 2 doses followed by a booster in 10 studies, (68.6%), 64 (0.8%) received 3 doses without a booster in 2 studies, and 2318 received a 3+1 schedule (30.6%) in 8 studies. A total of 159 vaccine failure cases were identified, representing 2.1% [95% CI: 1.8-2.4%] of the reported IPD cases. Most studies did not report clinical characteristics or outcomes. Among eight studies reporting comorbidities, 33/77 patients (42.9%) had an underlying condition. The main serotypes associated with vaccine failure were 19F (51/128 cases with known serotype; 39.8%), 6B (33/128; 25.8%), and 4 (10/128; 7.8%). Only five studies reported patient outcomes, with a crude case fatality rate of 2.4% (2/85; 95%CI: 0.3-8.5%).

CONCLUSION

Pneumococcal conjugate vaccines have been implemented in national immunisation programmes for more than a decade, yet there are only a few studies reporting vaccine failure. PCV failure is rare, irrespective of vaccine or schedule. Co-morbidity prevalence was high amongst vaccine failure cases but case fatality rate was relatively low. There is a need for more systematic reporting vaccine failure cases in countries with established pneumococcal vaccination programmes.