There are several risk factors associated with the development of infection following stroke. These include characteristics of study population (for example, patients in intensive care units), stroke severity, decreased conscious level, presence of dysphagia, advancing age, female gender, and diabetes mellitus. The list below outlines the factors associated with the development of chest infections (pneumonia) after stroke.

In clinical practice, it is fairly common for no causative organism to be detected in post-stroke pneumonia. This is due to difficulty in collecting sputum or aspirate for culture due to neurologic deficit or lowered level of consciousness, some cases of suspected pneumonia actually being non-infectious aspiration pneumonitis, or infection could be caused by anaerobic bacteria that require special culturing techniques [1]. A systematic review that examined the data of patients with post-stroke pneumonia to identify microorganisms reported that the organisms were mainly those associated with early onset nosocomial pneumonia, or a community acquired aspiration syndrome [1]. These included Streptococcus species, Staphylococcus aureus and gram-negative bacteria such as Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli or Enterobacter species. Gram-negative bacteria and Staphylococcus aureus are known to cause pneumonia by aspiration of endogenous material from the colonized oropharynx and are often seen in nosocomial infections [24]. Streptococcus species is still the most detected pathogen in community acquired pneumonia [25]. In stroke patients, it could be a cause of ‘community acquired aspiration pneumonia’, with aspiration occurring at the time of stroke [26].

Infections following stroke are associated with worse short-term and long-term outcomes. In pooled analyses by Westendorp et al., the mortality rate in patients with infection was 48 % versus 18 % in patients without infection [1]. Kwan et al. conducted a study of 439 patients (398 with stroke and 41 with transient ischaemic attack) exploring the clinical consequences of post-stroke infections [27]. They found that patients with post-stroke infections were more likely to develop other complications such as pressure sores and seizures. Furthermore, post-stroke infections were significantly associated with in-hospital mortality and institutionalization on discharge [27]. In a consecutive cohort study that looked at 521 acute stroke patients, stroke-associated infection was independently associated with poor functional outcome at discharge and at 1 year [28]. Pneumonia is the most common post-stroke infection and has been associated with a relative risk of 3.0 for mortality in a study of 14,293 patients with stroke [15]. In pooled analyses of effects of infection on outcome after stroke, pneumonia was significantly associated with in-hospital mortality [1]. Mortality rates were also higher in patients with pneumonia (26 % vs. 5 %) than those without pneumonia [1]. Post-stroke pneumonia also increases the financial burden on the medical system, with the annual cost of this complication reported to be about $459 million US [14].

Stott et al. found that in a study of 412 stroke patients, UTI was associated on univariate analysis with an increased risk of death and/or post-stroke disability at 3 months after stroke [2]. They postulated biologically plausible reasons for UTI causing a worse outcome after stroke: (1) During the acute phase of a UTI, UTI-induced systemic inflammation and raised temperature may cause further damage to vulnerable brain tissue in the ischaemic penumbra [29–31]. (2) Infections are associated with a catabolic response, with loss of skeletal muscle; this is likely to be due to multiple complex factors, including inflammation and cytokine release, increased glucocorticoids and activation of the sympatho-adrenal axis [32]. The associated loss of skeletal muscle is likely to adversely affect physical rehabilitation.

There are various recommendations that can reduce the prevalence of urinary tract infection (UTI) following stroke. Usual methods for preventing UTI are adequate hydration, use of cranberry juice, and oestrogen supplementation (topical) [35]. In hospitalized patients, other strategies include improving mobility with physiotherapy, preventing constipation, and avoiding or minimising the use of urinary catheters [35]. Minimising and avoiding unnecessary catheterization is probably the single most effective strategy in preventing UTI [36]. In certain circumstances it is necessary to use a urinary catheter, such as in acute urinary retention due to urethral obstruction (enlarged prostate, stone) or neurogenic bladder (stroke, multiple sclerosis, spinal injury), urological surgery, to allow healing of sacral pressure sores, and accurate measurement of urine output in critically ill patients [37]. It may be possible to reduce the risk of associated infection by early removal, vigilance in catheter-care, or by use of modified catheters coated with antimicrobials. A structured reminder to nurses by physicians to remove unnecessary catheters in ICU has been shown to reduce duration of catheterization and associated infections [38]. High aseptic standards of catheter care, correct positioning of the drainage tubing and collection bag, and maintaining a closed system may all help to reduce the risks of clinically significant infection [39]. Using modified catheters such as nitrofurazone-coated silicone or silver-coated latex may reduce the risk of infection with short-term catheterization [39, 40].

Bearing in mind that aspiration is an important risk factor for chest infection after stroke, appropriate management of dysphagia following stroke is vital in reducing chest infections. A strict vigilant swallowing assessment after stroke is important. The most widely accepted measure is to keep a stroke patient nil by mouth until the swallow has been formally assessed [41]. Formal swallow assessment including a water swallow assessment also significantly reduces the risk of pneumonia [42, 43]. It has been shown that patients having intensive (daily) standard swallow therapy developed fewer chest infections secondary to aspiration compared to those receiving usual care (26 % vs 47 %) [44]. Nasogastric feeding or percutaneous gastrostomy tube are common ways of providing nutrition to stroke patients who have an unsafe swallow. However, these methods do not eliminate the occurrence of pneumonia, since aspiration of oral contents may continue [45]. A recent Cochrane review of the clinical trials showed no difference between these two methods regarding the occurrence of pneumonia in patients with dysphagia; however, percutaneous gastrostomy tube was safer and more effective in terms of feeding [46]. Regular oral hygiene is also important in reducing the development of chest infections.