Invasive Staphylococcus aureus infections

Abstract

Staphylococcus aureus is a leading cause of septicaemia-related death. The aims of this thesis were to describe the epidemiology of invasive Staphylococcus aureus infections (ISA), the clinical course, and serological response in ISA in a prospective, population-based study. The antibody response was compared with the serological findings in healthy individuals.

During two years 170 episodes of ISA were registered, with an incidence of 33.9 cases/100,000/year. Haemodialysis (relative risk 291) and peritoneal dialysis (relative risk 204) patients were at the highest risk. Soft tissue infections, bacteraemia without focus, infections of intravenous lines, and joint/bone infections were the most common diagnoses. The spectrum of signs and symptoms was wide, with nearly a quarter of the patients being afebrile.

The mortality rate was 19.1% (28-day mortality), with an annual population mortality of 5.9/100,000. Patients with complicated bacteraemia (32% of all episodes) had a mortality rate of 32%, and patients with severe sepsis (30% of all episodes) 54%. Patients with bacteraemia without focus, patients with respiratory infections, and patients with endovascular infections had the highest mortality figures . Only severe sepsis and low systolic blood pressure were independent factors for mortality in a multivariable regression model. We found a relapse rate of 9.3%, and a rate of remaining symptoms after the antibiotic treatment had ended of 34%. Sequelae were seen among 60% of the patients with arthritis. The frequency of different agr, accessory gene regulator, groups was not correlated to the disease entities.

The antibody response in ISA showed a great variability. Patients with a fatal outcome produced lower amounts of antibodies to all antigens, and significantly to four antigens (teichoic acid, lipase, enterotoxin A, and scalded skin syndrome toxin). The same trend was noted for patients with a complicated course of infection.

Healthy carriers of S. aureus in the nares had higher levels of antibodies to all eleven tested antigens, and significantly to five, than non-carriers. Ages over 65y showed only slightly lower levels.