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A lung abscess is a cavity with a well-defined wall that develops in the lung due to microbial infection. This most commonly occurs with polymicrobial aerobic and anerobic infections related to aspiration pneumonia. Lung abscess may also be related to necrotizing pneumonia from aerobic organisms (eg, Staphylococcus aureus, Pseudomonas aeruginosa), septic emboli, or bronchial obstruction (eg, tumor). Most patients respond to appropriate antimicrobial therapy. However, catheter or surgical drainage may be needed if initial therapy is ineffective or the patient has complications such as extension into the pleural space (empyema). Pleural effusion is a manifestation of various underlying pathologies with a broad differential diagnosis. Defining the etiology of pleural effusion is critical for appropriate management. Thoracentesis should be considered for all pleural effusions associated with pneumonia. Parapneumonic effusions and empyema should be treated with prompt initiation of antibiotics and drainage of infected pleural fluid.

Community-acquired pneumonia (CAP) is a common and potentially serious illness, particularly in older patients and those with significant comorbidities. Recent evidence indicates diverse communities of microbes reside within the alveoli as part of the lung microbiome and may play a role in the development of pneumonia. A CAP diagnosis is based on the demonstration of a new infiltrate on imaging in a patient with symptoms and signs of pneumonia. Although vaccination has decreased its incidence, Streptococcus pneumoniae (pneumococcus) remains the most common bacterial cause of CAP. Macrolide resistance to S pneumoniae has increased in the United States. With their increasing availability, newer molecular testing methods (eg, respiratory pathogen polymerase chain reaction panel) play a significant role in the evaluation of respiratory viruses. Antimicrobial therapy for hospitalized patients should be based on the results of diagnostic studies to allow pathogen-directed therapy and optimal antimicrobial stewardship. The recommended duration for antimicrobial therapy is 3 to 5 days if there is good clinical improvement by day 2 or 3. Procalcitonin levels can be useful as an adjunct to clinical judgment for determining the appropriate duration of therapy. Smoking cessation and vaccination should be prioritized because they significantly reduce the incidence and severity of CAP.

Nosocomial pneumonia, which includes hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP), is associated with high morbidity and mortality. HAP occurs 48 hours or more after admission and may require intubation and mechanical ventilation. VAP occurs more than 48 hours after mechanical ventilation is initiated. The mortality rate of VAP and ventilated HAP ranges from 15% to 30%, depending on severity. Diagnosis is based on a new pulmonary infiltrate associated with clinical evidence of infection such as new-onset fever, purulent sputum, leukocytosis, and decline in oxygenation. Optimal management includes identification of the causative pathogen, early empiric antimicrobial therapy directed against likely pathogens, and de-escalation of treatment once a pathogen is identified. The standard treatment duration is 7 days for patients who are improving clinically. Effective methods to prevent VAP include washing hands adequately between patient contacts, maintaining semirecumbent patient positioning, avoiding gastric overdistention, providing continuous subglottic suctioning for patients on mechanical ventilation, limiting stress-ulcer prophylaxis, and practicing daily oral care with toothbrushing.

Immunocompromised patients with pneumonia can have infection with both common pulmonary pathogens and opportunistic pathogens. A basic microbiological workup should be performed in all immunocompromised patients who are hospitalized and considered for outpatients. The need for a more extensive and invasive workup (eg, bronchoscopy for bronchoalveolar lavage transbronchial lung biopsy) should be individualized, considering risk factors for opportunistic pathogens. As part of treating immunocompromised patients with pneumonia, it is important to evaluate whether any immunosuppressive medications can be discontinued or decreased to improve the patient's level of immunity. Empiric therapy for opportunistic pathogens should be considered in patients who have risk factors for a particular pathogen and when delaying appropriate therapy would increase mortality risk.

Heart murmurs are common in childhood. Any murmur associated with cardiac signs or symptoms should be referred to a pediatric cardiologist for further evaluation. A benign murmur typically can be differentiated from a pathologic murmur based on its characteristics. Between 1% and 5% of newborns and infants will have a murmur, and up to 50% of those will be due to a structural defect. Congenital heart disease is the most common diagnosis in newborns and infants with a murmur, but a majority of congenital heart disease lesions diagnosed in asymptomatic infants and children will be minor and resolve with time. Although up to 50% of children will have a murmur at some time in their life, less than 30% of murmurs referred to pediatric cardiologists are pathologic. In older children, undiagnosed congenital heart disease is much less common than cardiomyopathies and acquired valvular disease, which are important causes of pathologic murmurs. Echocardiography is the preferred imaging modality for evaluating murmurs.

The purpose of the cardiac portion of the preparticipation physical evaluation is to identify potential health risks in young athletes, particularly sudden cardiac death. The preparticipation evaluation begins with a detailed screening questionnaire. Sudden cardiac death in athletes is considered rare, but the incidence in athletes is higher than in the general population. Leading causes of sudden cardiac death include hypertrophic cardiomyopathy, coronary artery anomalies, myocarditis, arrhythmogenic right ventricular cardiomyopathy, and aortic dissection. It also can be due to ventricular fibrillation, sometimes preceded by ventricular tachycardia. Electrocardiogram results may be abnormal in athletes who are at risk for sudden cardiac death, but diagnosis is made using cardiac imaging. Guidelines exist with recommendations for return to play for athletes who are at risk for sudden cardiac death.

Cardiac dysrhythmias in children can be due to a structural abnormality or an intrinsic defect in the electrical conduction system of the heart. In a child with a structurally normal heart, the mechanisms for dysrhythmias are the same as in adults, although the incidence and prevalence are different. Supraventricular tachycardias (SVTs) originate above the ventricles. In children, the two peak ages of onset for SVT are from before birth through the first year of life, and from ages 6 to 8 years. In most cases, there is spontaneous clinical resolution within the first year. When treatment is necessary, it includes vagal maneuvers, pharmacotherapy, and ablation. Wolff-Parkinson-White syndrome is a type of reentrant SVT that involves an accessory pathway. Long QT syndrome is a prolongation of the QT interval due to a genetic channelopathy. Bradycardia and heart block can be due to maternal autoimmune antibodies or structural heart defects. Ventricular tachyarrhythmias can be due to underlying structural heart disease, cardiomyopathy, or a metabolic derangement and may lead to sudden cardiac death.

Kawasaki disease is an acute vasculitis of unknown etiology that primarily affects children younger than 5 years, although it can affect older children. Cardiac complications are the major cause of morbidity and mortality in Kawasaki disease and can include myocarditis. Long-term sequelae include coronary artery dilation. Treatment is high-dose intravenous immunoglobulin and aspirin. Multisystem inflammatory syndrome in children (MIS-C) is a severe hyperinflammatory syndrome associated with COVID-19 disease. It shares clinical characteristics with Kawasaki disease but causes hyperinflammation and often results in cardiac dysfunction. Treatment for MIS-C is intravenous immunoglobulin and glucocorticoids. Myocarditis is inflammation of the myocardium and pericardium and has multiple causes. It is associated with COVID-19 infection and mRNA COVID-19 vaccines. The incidence and clinical significance of these associations remain uncertain and are a current topic of research and debate.