Fever, chest pain, malaise, cough, dyspnea and purulent sputum are clinical signs of pneumonia and pleuritic chest pain, a more specific sign of pleural involvement, may be reported as well, but its absence does not exclude the presence of a parapneumonic effusion  . Apart from weakness, elderly patients may not report any additional symptoms , which is why a meticulous assessment must be performed to exclude life-threatening pulmonary infection.
A thorough physical examination is the first step, followed by imaging studies that will identify fluid in the pleural space. Radiography, ultrasonography, or CT can be used for visualization of the effusion, but the mainstay of diagnosis is thoracentesis - the sampling of pleural fluid through the thorax . Subsequent analysis of the aspirate for its acidity, presence of leukocytes, CRP, LDH and bacteria is performed and should be mandatory for every patient in whom pleural effusions develop due to pneumonia  .
Intravenous antibiotic therapy may be recommended for uncomplicated PPE, but in many patients, the therapeutic effects of thoracentesis have been well-documented and the procedure is often used for both diagnostic and therapeutic purposes  . For severe PPE, chest tube drainage is favored, while the role of fibrinolytic in treatment of PPE was evaluated across many studies and their administration seems to facilitate drainage of excess pleural fluid due to resolution of thrombi in the local circulation  . For empyemas and severe effusions, surgical procedures such as thoracoscopy, standard thoracotomy and video-assisted thoracic surgery are favored  .
A parapneumonic effusion significantly increases mortality rates of pneumonia, as its occurrence potentiates a more severe form of pulmonary infection. Empyema carries a mortality rate of 5-30% depending on the presence of comorbidities, while in immunocompromised hosts, a mortality rate of 40% was established . For this reason, an early diagnosis is detrimental in preventing disease progression and to ensure proper treatment in its initial stages.
Parapneumonic effusions are primarily caused by streptococcal (S. pneumoniae, S. pyogenes, and the S. anginosus group) and staphylococcal (S. aureus, both methicillin-sensitive and methicillin-resistant strains) species, while gram-negative bacilli (klebsiella pneumoniae, pseudomonas aeruginosa) have also been described as underlying pathogens .
Approximately 1 million patients are hospitalized due to pneumonia in the United States and between 20-57% develop parapneumonic effusion, while 5-10% develop empyema, considered to be the end-stage of parapneumonic effusion . Immunocompromised patients have shown to be at an increased risk for PPE, whereas cigarette smoking and alcohol consumption promote aspiration of oropharyngeal microorganisms .
In the majority of cases, the initial pulmonary infection stems from aspiration of bacteria residing in the oropharynx and subsequent development of pneumonia . After 2-5 days of microbial spread and disruption of the capillary endothelium, effusion of fluid into the pleural space may occur as a complication of the infection. If left untreated, the progressive clinical course may result in secretion of pus in the pleural space and the formation of an abscess, termed empyema .
Effusion of fluid or formation of pus in the pleural space as a result of pneumonia is termed parapneumonic effusion (PPE) . Streptococcus pneumoniae, streptococcus pyogenes, streptococcus anginosus and staphylococcus aureus are most frequent causative agents and up to 50% of patients suffering from pneumonia develop this complication, depending on the presence of comorbidities and the status of the immune system . The main clinical symptoms are pleuritic chest pain, fever, cough, expectoration of purulent sputum and dyspnea . The initial diagnosis can be made clinically, but imaging studies (X-ray, ultrasound or computed tomography (CT)) and laboratory workup (leukocyte count, lactate dehydrogenase (LDH) and C-reactive protein (CRP)) are necessary for confirmation  . Thoracentesis, however, is the gold standard in the diagnosis of parapneumonic effusion . Treatment strategies include drainage of accumulated fluid through either blind or image-guided catheter placement, open thoracotomy or video-assisted thoracoscopic surgery .
The term parapneumonic effusion describes the leakage of fluid into space between two layers of pleura (a thin membrane covering the lungs) caused by more severe forms of pneumonia. In most cases, streptococcal and staphylococcal bacteria are causative agents of pneumonia, that has shown to be responsible for over 1 million hospitalizations in the United States every year. Between 20-57% of patients develop parapneumonic effusion and this complication may substantially increase mortality rates of pneumonia if not recognized on time. For this reason, why symptoms such as fever, cough, breathing difficulties and chest pain should not be taken lightly. X-rays or ultrasound may reveal the presence of fluid in the pleural space, but to confirm the infection, a sample of fluid is aspirated during a procedure known as thoracentesis, after which it is tested for the level of acidity and the quantity of glucose, white blood cells, and bacteria. Treatment depends on the severity of effusion, ranging from antibiotics and aspiration of fluid to open surgery to remove the fluid.