Bacteraemia, Septicaemia, and Endocarditis

I know I've been doing a lot of pathology, but it's the pathology lectures I've been struggling with most, so here we are. Of course, if there's anything that you want me to cover, let me know in the comments and I'll get to it when I have time (ha!). In the meantime, some of the other topics that we've covered this year (such as physiology and some of the micro stuff) are also covered in some of my earlier blog posts, so you can use the search bar to (hopefully) find what you need :)

Define sepsis and bacteraemia

Sepsis is when a dysregulated immune response to an infection (e.g. inability of the immune system to contain the infection) results in life-threatening organ dysfunction. Bacteraemia, on the other hand, is simply the presence of bacteria in the blood.

Understand the key clinical issues around sepsis and bacteraemia

Sepsis

Sepsis, as you are probably well aware, is not a good state to be in. Patients who are in sepsis may have rigors (extreme shivering), fever, delirium, dyspnea, and many other fun symptoms. Even after the illness is over, patients may be immunosuppresed for some time afterwards, increasing their susceptibility to other infections.

The severity of sepsis can be measured using assessment tools such as the qSOFA. The qSOFA simply looks at 3 different criteria: a systolic blood pressure lower than 100mmHg, an altered mental status, and a respiratory rate faster than 22 per minute. The more criteria a patient meets, the worse their outcome. The actual cause of infection can be detected in the usual ways (blood/urine culture, imaging, and so on).

To treat sepsis, you need to provide supportive care to the host (fluids, ventilation if required, etc.), and give antimicrobial therapy to treat the causative agent. Also, any infected catheters etc. should be removed.

To prevent sepsis, you basically just have to use the same infection control measures that you'd use for anything. This includes handwashing and being mindful of catheters and other devices that are being inserted into patients. Keeping up-to-date with immunisations helps too.

Bacteraemia

Bacteraemia can be classified according to how frequently and how persistent the bacteraemia is. If bacteraemia is only transient, like what happens when you brush your teeth, it is transient bacteraemia. If the bacteraemia repeatedly comes and goes for short bursts at a time, it is likely from a focus of infection, such as an abscess. If the bacteraemia persists for a while, the source of infection is likely in the bloodstream.

Bacteraemia can be tested for by using blood culture bottles (see here). When collecting specimens, care must be taken to avoid contamination of the sample. Blood is often taken from 2-3 sites to make it easier to tell what is a contaminant and what is the causative agent. After bacteria have been cultured, they can be identified. Since sepsis is pretty life-threatening, rapid methods such as MALDI-TOF (see here) are preferred.

Define endocarditis

Endocarditis is infection of the endocardial surfaces of the heart, such as the valves. It is mostly left-sided but can also be right-sided (IV drug users are most likely to have right-sided infectious endocarditis). Endocarditis can be classified into acute, subacute, and chronic endocarditis. Acute endocarditis can kill within 6 weeks, chronic endocarditis takes longer than 3 months to kill, and subacute is somewhere in between.

Understand and discuss the aetiology, pathogenesis and pathophysiology, clinical features and treatment principles for infective endocarditis

Aetiology

The main causative agents of acute endocarditis include S. aureus, S. pneumoniae, and N. gonorrhoeae. The main causative agents of chronic endocarditis include Viridians streptococci, the "HACEK" group of bacteria (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella), and Enterococcus.

People who have some kind of heart disease or history of previous infectious endocarditis are most likely to get endocarditis.

Pathogenesis and Pathophysiology

Bacteria adhere to and colonise the endocardium, something something something. There's not very much in the lecture slides on this so I'm just going to leave it there and move on :)

Clinical Features

There are a range of complications associated with infective endocarditis. The complications that are most likely to lead to death are cardiac complications, which include valve destruction and abscesses. Emboli may also occur, as may metastatic abscesses and immunological complications such as deposition of immune complexes. There may also be sepsis.

Treatment Principles

To diagnose endocarditis, you can use bacterial cultures and echocardiogram. Imaging may also help to detect complications. Treatment is primarily through antibiotics and surgery. The exact antibiotic regimen depends on the causative agent, but usually around six weeks of intravenous antibiotics are required. Most surgery is valve replacement surgery.

As for prevention, it is common practice to give prophylaxis prior to dental procedures in patients considered to be at high risk of endocarditis. Prophylaxis generally takes the form of amoxycillin, but there are alternatives that can be used if the patient is allergic to penicillin.