Pneumococcal disease burden, clinical presentations and vaccine coverage in the Jamaican population.

BACKGROUND: Pneumococcal serotypes circulating in any population vary over time and between countries and impacts the effectiveness of pneumococcal vaccination. OBJECTIVE: This study investigated the epidemiology of pneumococcal disease in Jamaica. METHODS: Streptococcus pneumoniae isolates (n= 349) along with demographic and clinical information were collected from patients presenting at the 4 major hospitals in Jamaica over a 2-year period. Serotyping was done using latex agglutination tests and the Quellung reaction assay. RESULTS: Invasive pneumococcal disease (IPD) incidence was 45.4/100,000 in children under 5 yrs and 16.3/100,000 in adults over 65 yrs. Thirteen serogroups were identified among the 120 isolates subjected to grouping; the most common being serogroups: 19 (22/120,18.3%), 6 (20/120,16.7%), 14 (20/120,16.7%), 23 (18/120,15.0%), 3 (11/120,9.2%) and nontypeable (8/120,2.3%). The estimated vaccine coverage rates for the PCV7 and PCV13 vaccines in children less than 5 yrs were 82.5% and 88.7% respectively. The 23-valent PPV23 provided 100% coverage rate in adults over 65 yrs and 82.9% coverage rate for the entire population. CONCLUSIONS: Pneumococcal vaccine coverage rates in Jamaica are comparable to those reported in certain developed countries and higher than in other developing countries. The high incidence of IPD in the paediatric population indicates that routine vaccination would be beneficial.

Brazil nut effect and excluded volume attraction in vibrofluidized granular mixtures.

A two dimensional bi-disperse vibrofluidized granular mixture is studied in the rapid flow regime, where particle interactions occur due to instantaneous collisions. Both experiments and simulations are carried out, and these show the existence of two phenomena which have been observed only in very dense granular flows or in equilibrium systems. The Brazil nut phenomenon, which involves the rise of larger particles in a granular mixture upon vibration, has been observed in dense systems due to the percolation of small particles though the interstitial spaces between the large particles, or due to convection rolls. In the present case, where neither effect is present, it is observed that the fluidization of the smaller particles by vibration results in an exponentially decaying density profile, at heights large compared to the particle diameter, and thereby a pressure field that decreases with height. The larger particles, suspended in this decaying pressure field, experience a larger pressure at the bottom and a smaller pressure on top, and they rise to a height where the net force caused by the decreasing pressure is balanced by the weight of the particle. An attractive force between the large particles, similar to the entropic attraction effect in mixtures of colloids and polymers, is also observed in this nonequilibrium system, because when the distance between the large particles is less than the small particle diameter, the pressure between the large particles is smaller than that on the outside. Analytical results are derived for each of these effects, and these are in agreement with the experimental and simulation results.