A 9-month-old girl is brought to the emergency department due to fever and cough. Her symptoms began approximately 2 days ago and have been worsening. The patient is otherwise healthy except for an episode of acute otitis media 3 weeks ago that resolved following a course of oral amoxicillin. She lives with her mother, father, and grandmother who have been in good health. Her mother smokes cigarettes. Temperature is 38.5 C (101.3 F) and respirations are 34/min. Pulse oximetry is 95% on room air. Pulmonary examination reveals mild subcostal retractions and focal crackles in the left lower lobe. Which of the following underlying factors is most likely contributing to this patient's current condition?

Question

A 9-month-old girl is brought to the emergency department due to fever and cough.  Her symptoms began approximately 2 days ago and have been worsening.  The patient is otherwise healthy except for an episode of acute otitis media 3 weeks ago that resolved following a course of oral amoxicillin.  She lives with her mother, father, and grandmother who have been in good health.  Her mother smokes cigarettes.  Temperature is 38.5 C (101.3 F) and respirations are 34/min.  Pulse oximetry is 95% on room air.  Pulmonary examination reveals mild subcostal retractions and focal crackles in the left lower lobe.  Which of the following underlying factors is most likely contributing to this patient's current condition?

Quizplus · Accepted Answer

11ec160b_3a0a_2f65_9249_d79e51f33ca2_MD0001_00 This patient has fever, cough, and focal crackles, which are findings consistent with pneumonia. Transmission typically occurs via droplet spread of a bacterium (eg, Streptococcus pneumoniae) with subsequent colonization of the nasopharynx and microaspiration into the lungs. Respiratory defense mechanisms often prevent infection of the lower respiratory tract, and the first line of defense is the ciliated epithelium and mucus-producing cells that line the respiratory tract. Pathogens become entrapped in mucus and are transported upward and out of the nasopharynx by the sweeping cilia. Other defense mechanisms include binding by immunoglobulin (eg, secretory IgA, opsonizing IgG and IgM), phagocytosis by alveolar and interstitial macrophages, and cell-mediated cytotoxic activity. Secondhand smoke exposure disrupts natural host defenses and increases the risk of pneumonia, particularly in infants who have a parent that smokes. Cigarette smoke induces mucus overproduction and impairs ciliary function, leading to delayed clearance of pathogens and respiratory secretions. In addition to respiratory infections, children with secondhand smoke exposure are also at increased risk for asthma and wheezing and are more likely to have recurrent otitis media. (Choice A) A decreased number of monocytes may occur with bone marrow dysfunction, which would typically cause severe, disseminated infections (not seen in this patient). In addition, although the phagocytic function of alveolar macrophages (differentiated type of monocyte) is impaired in patients with cigarette smoke exposure, these cells are typically present in increased (not decreased) numbers. (Choice B) Although cigarette smoke exposure is associated with increased risk of asthma, airway hyperreactivity causes bronchoconstriction and wheezing, not pneumonia as seen in this patient. (Choice D) Inhibited B cell maturation, as seen with X-linked agammaglobulinemia, typically presents with recurrent sinopulmonary infections in young boys, not girls. In addition, cigarette smoke can increase (not decrease) IgE production due to allergic sensitization. (Choice E) Reduced alveolar surface area occurs with emphysema, which is a late lung finding in patients who smoke. Emphysema would not be present in infancy and does not cause pneumonia. Educational objective: Infants with secondhand smoke exposure are at increased risk for pneumonia because cigarette smoke affects alveolar macrophage function and impairs mucociliary clearance. __________ References: Secondhand smoke induces inflammation and impairs immunity to respiratory infections. (http://www.ncbi.nlm.nih.gov/pubmed/29555783)

A 9-Month-Old Girl Is Brought to the Emergency Department Due