IV-74. The answer is B. (Chap. 143) Close contacts of individuals with meningococcal disease are at increased risk of developing secondary disease with reports of secondary cases in up to 3% of primary cases. The rate of secondary cases is highest during the week after presentation of the index case with most cases presenting within 6 weeks. Increased risk remains for up to 1 year. Prophylaxis is recommended for persons who are intimate or household contacts of the index case and health care workers who have been directly exposed to respiratory secretions. Mass prophylaxis is not usually offered. The aim of prophylaxis is to eradicate colonization of close contacts with the strain that has caused invasive disease. Prophylaxis should be given as soon as possible to all contacts at the same time to avoid recolonization. Waiting for culture is not recommended. Ceftriaxone as a single dose is currently the most effective option in reducing carriage. Rifampin is no longer the optimal agent because it requires multiple doses and fails to eliminate carriage in up to 20% of cases. In some countries, ciprofloxacin or ofloxacin is used, but resistance has been reported in some areas. Current conjugated vaccines do not include N. meningitides serotype B. Most sporadic cases in the United States are now caused by this serotype. Vaccination should be offered in cases of meningococcal disease caused by documented infection by a serotype included in the current vaccine.
IV-75. The answer is D. (Chap. 144) Because of emerging resistance, treatment recommendations for gonorrhea require frequent updating. Fluoroquinolones and penicillin are no longer generally recommended in the United States because of resistance. Current effective therapies use single-dose therapies to maximize adherence. Oral cefixime or intramuscular ceftriaxone are effective for urethritis, cervicitis, and proctitis. Azithromycin is no longer effective for gonorrhea because of resistance, but it should be administered because of the presumption of chlamydial co-infection. Doxycycline also an option for co-treatment in nonpregnant women. Patients with uncomplicated infection who receive therapy do not require a test of cure. Patients should be instructed to contact sexual partners for screening and therapy. Recent studies have demonstrated that the provision of medications or
prescriptions to treat gonorrhea and chlamydia in sexual partners diminishes the risk of reinfection in the affected patient.
IV-76. The answer is D. (Chap. 145) Generally thought of as a disease of children, epiglottitis is also a disease of adults since the wide use of Haemophilus influenzae type B vaccination. Epiglottitis can cause life-threatening airway obstruction caused by cellulitis of the epiglottis and supraglottic tissues, classically caused by H. influenzae type B infection. However, other organisms are also common causes, including nontypeable H. influenzae, Streptococcus pneumoniae, H. parainfluenzae, Staphylococcus aureus, and viral infection. The initial evaluation and treatment for epiglottitis in adults includes airway management and intravenous antibiotics. The patient presented here is demonstrating signs of impending airway obstruction with stridor, inability to swallow secretions, and use of accessory muscles of inspiration. A lateral neck radiograph shows the typical thumb sign indicative of a swollen epiglottis. In addition, the patient has evidence of hypoventilation with carbon dioxide retention. Thus, in addition to antibiotics, this patient should also be intubated and mechanically ventilated electively under a controlled setting because he is at high risk for mechanical airway obstruction. Antibiotic therapy should cover the typical organisms outlined above and include coverage for oral anaerobes.
In adults presenting without overt impending airway obstruction, laryngoscopy would be indicated to assess airway patency. Endotracheal intubation would be recommended for those with more than 50% airway obstruction. In children, endotracheal intubation is often recommended because laryngoscopy in children has provoked airway obstruction to a much greater degree than adults, and increased risk of mortality has been demonstrated in some series in children when the airway is managed expectantly.
IV-77. The answer is A. (Chap. 145) Moraxella catarrhalis is an unencapsulated gram-negative diplococcus that causes upper respiratory tract disease in children and adults. Some studies suggest that the widespread implementation of pneumococcal vaccination has increased the prevalence of M. catarrhalis and related organisms as a cause of disease. M. catarrhalis causes approximately 10% to 20% of cases of otitis media in children, often after a preceding viral infection. It is the second most common proven bacterial cause of chronic obstructive pulmonary disease (COPD) exacerbations after Haemophilus influenzae. Clinical features do not distinguish among the various bacterial and viral causes of COPD exacerbations. In most cases, a proven cause is not found. Currently, most strains of M. catarrhalis demonstrate β-lactamase activity. Recommended therapy includes agents effective for upper respiratory, sinus, and otic infections presumed to be caused by M. catarrhalis, H. influenzae, a n d S. pneumoniae, including amoxicillinľclavulanic acid, extended-spectrum cephalosporins, azithromycin, clarithromycin, and flouroquinolones.
IV-78. The answer is C. (Chap. 146) This patient has subacute bacterial endocarditis caused by infection with one of the HACEK organisms. The HACEK organisms (Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella spp.) are gram-negative rods that reside in the oral cavity. They are responsible for about 3% of cases of infective endocarditis in most series. They are the most common cause of gram-negative endocarditis in nondrug abusers. Most patients have a history of poor dentition or a recent dental procedure. Often, patients are initially diagnosed with culture-negative endocarditis because these organisms may be slow growing and fastidious. Cultures must be specified for prolonged culture of fastidious organisms. HACEK endocarditis is typically subacute, and the risk of embolic phenomena to the bone, skin, kidneys, and vasculature is high. Vegetations are seen on
approximately 85% of transthoracic echocardiograms. Cure rates are excellent with antibiotics alone; native valves require 4 weeks, and prosthetic valves require 6 weeks of treatment. Ceftriaxone is the treatment of choice, with ampicillinľgentamicin as an alternative. Sensitivities may be delayed because of the organismsĺ slow growth.
IV-79. The answer is B. (Chap. 146) Capnocytophaga canimorsus is the most likely organism to have caused fulminant disease in this patient with alcoholism after a dog bite. Patients with a history of alcoholism, asplenia, and glucocorticoid therapy are at risk of developing disseminated infection, sepsis, and disseminated intravascular coagulation. Because of increasing β-lactamase expression, recommended treatment is with ampicillinľsulbactam or clindamycin. One of these therapies should be administered to asplenic patients with a dog bite. Other species of Capnocytophaga cause oropharyngeal disease and can cause sepsis in neutropenic patients, particularly in the presence of oral ulcers. Eikenella and Haemophilus spp. are common mouth flora in humans but not in dogs. Staphylococcus spp. can cause sepsis but is less likely in this scenario.
IV-80. The answer is B. (Chap. 147) Despite antibiotic treatment, pneumonia from all causes remains a major source of mortality in the United States. Mortality from Legionella pneumonia varies from 0% to 11% in treated immunocompetent patients to about 30% if not treated effectively. Because Legionella spp. is an intracellular pathogen, antibiotics that reach intracellular MICs are most likely to be effective. Newer macrolides and quinolones are antibiotics of choice and are effective as monotherapy. Doxycycline and tigecycline are active in vitro. Anecdotal reports have described successes and failures with trimethoprimľsulfamethoxazole and clindamycin. Aztreonam, most β-lactams, and cephalosporins cannot be considered effective therapy for Legionella pneumonia. For severe cases, rifampin may be initially added to azithromycin or a fluoroquinolone.
IV-81. The answer is C. (Chap. 147) Legionella is an intracellular pathogen that enters the body through aspiration or direct inhalation. Numerous prospective studies have found it is one of the four most common causes of community-acquired pneumonia with Streptococcus pneumoniae, Haemophilus influenzae, and Chlamydia pneumoniae accounting for 2% to 9% of cases. Postoperative patients are at risk because of an increased risk of aspiration. Cell-mediated immunity is the primary host defense against Legionella spp., and patients with HIV or those who take glucocorticoids are at risk based on their depressed cell-mediated immune function. Alveolar macrophages phagocytose Legionella spp. Smokers and those with chronic lung disease are at risk given their poor local immune responses and decreased ability for widespread phagocytosis. Neutrophils play a comparatively small role in the host defense against Legionella spp., and those with neutropenia are not predisposed to Legionella infection.
IV-82. The answer is D. (Chap. 147) Legionella urine antigen is detectable within 3 days of symptoms and will remain positive for 2 months. It is not affected by antibiotic use. The urinary antigen test is formulated to detect only L. pneumophila (which causes 80% of Legionella infections) but cross-reactivity with other Legionella spp. has been reported. The urinary test result is sensitive and highly specific. Typically, Gram staining of specimens from sterile sites such as pleural fluid show numerous white blood cells but no organisms. However, Legionella spp. may appear as faint, pleomorphic gram-negative bacilli. Legionella spp. may be cultured from sputum even when epithelial cells are present. Cultures, grown on selective media, take 3 to 5 days to show visible growth. Antibody detection using acute and convalescent serum is an accurate means of diagnosis. A fourfold rise is diagnostic, but this
takes up to 12 weeks, so it is most useful for epidemiologic investigation. Legionella polymerase chain reaction has not been shown to be adequately sensitive and specific for clinical use. It is used for environmental sampling.
IV-83. The answer is C. (Chap. 148) Pertussis caused by the gram-negative bacteria Bordetella pertussis, is an upper respiratory infection characterized by a violent cough. Its prevalence has been dramatically reduced, but not eliminated, by widespread infant vaccination. It causes an extremely morbid and often mortal disease in infants younger than 6 months old, particularly in the developing world. The prevalence appears to be increasing in young adults and adolescents because of waning immunity. Some are recommending booster vaccination after 10 years. B. pertussis is also a growing pathogen in patients with chronic obstructive pulmonary disease. The clinical manifestations typically include a persistent, episodic cough developing a few days after a cold-like upper respiratory infection. The cough may become persistent. It often wakes the patient from sleep and results in posttussive vomiting. An audible whoop is only present in fewer than half of cases. Diagnosis is with nasopharyngeal culture or DNA probe testing. There is no urinary antigen testing available. The goal of antibiotic therapy is to eradicate the organism from the nasopharynx. It does not alter the clinical course. Macrolide antibiotics are the treatment of choice. Pneumonia is uncommon with B. pertussis. Cold agglutinins may be positive in infection with Mycoplasma pneumoniae, which is on the differential diagnosis of B. pertussis.
IV-84. The answer is C. (Chap. 149) Enterotoxigenic Escherichia coli is the most common cause of travelerĺs diarrhea, accounting for 50% of cases in Latin America and 15% in Asia. Enterotoxigenic and enteroaggregative E. coli are the most common isolates from persons with classic secretory travelerĺs diarrhea. Bloody stools, fecal leukocytes, and fever are typically absent. Symptoms typically last less than 3 days. The spectrum of disease can range from mild to severe with life-threatening volume loss. Treatment of frequent watery stools caused by presumed E. coli infection with ciprofloxacin, or because of concerns regarding increasing ciprofloxacin resistance, azithromycin may shorten the duration of symptoms. Entamoeba histolytica and Vibrio cholerae account for smaller percentages of travelerĺs diarrhea in Mexico. Campylobacter infection is more common in Asia and during the winter in subtropical areas. Giardia infection is associated with contaminated water supplies and in campers who drink from freshwater streams.
IV-85. The answer is D. (Chap. 149) β-lactamases are a major source of antibiotic resistance in gram-negative bacilli. Many gram-negative bacteria produce broad-spectrum β-lactamases that confer resistance to penicillins and first-generation cephalosporins. The addition of clavulanate, a β-lactamase inhibitor, to an antibiotic regimen is often enough to overcome this resistance. Extended-spectrum β-lactamases (ESBLs), however, lead to resistance to all β-lactam drugs, including third- and fourth-generation cephalosporins. ESBL-producing genes can be acquired by gram-negative bacteria via plasmids and are becoming increasingly prevalent in hospitals worldwide. Klebsiella and Escherichia coli are the most common bacteria that acquire ESBLs, although it can be seen in many other gram-negatives, including Serratia, Proteus, Enterobacter, and Citrobacter spp. The most common scenario for the development of ESBL-gram negative organisms in the hospital is prevalent use of third-generation cephalosporins. Carbapenems should be considered first-line antibiotics for these bacteria. Macrolides and quinolones have different mechanisms of action than β-lactam antibiotics and do not apply selective pressure to generate ESBL-producing bacteria.
IV-86. The answer is B. (Chap. 149) E. coli is the etiologic agent in 85% to 95% of uncomplicated urinary tract infections (UTIs) that occur in premenopausal women. Uncomplicated cystitis is the most common UTI syndrome. About 20% of women will develop a recurrence in 1 year after their initial UTI. Pregnant women are at high risk of cystitis developing into pyelonephritis. Proteus infection represents only 1% to 2% of uncomplicated UTIs. Proteus infection causes 20% to 45% of UTIs in patients with long-term bladder catheterization. Klebsiella spp. also accounts for only 1% to 2% of uncomplicated UTIs; however, it is responsible for 5% to 17% of complicated UTIs. Enterobacter spp. is a rare cause of infection outside of the hospital. Candida spp. is most often a genitourinary colonizer in healthy patients and is rarely the cause of infection.
IV-87. The answer is A. (Chap. 149) Shiga toxic and enterohemorrhagic strains of Escherichia coli (STEC/EHEC) cause hemorrhagic colitis and hemolytic uremic syndrome (HUS). Several large outbreaks resulting from the consumption of fresh produce (e.g., lettuce, spinach, sprouts) and of undercooked ground beef have received significant attention in the media. O157:H7 is the most prominent serotype, but others have been reported to cause similar disease. The ability of STEC/EHEC to produce Shiga toxin (Stx2 and/or Stx1) or related toxins is a critical factor in the expression of clinical disease. Manure from domesticated ruminant animals in industrialized countries serves as the major reservoir for STEC/EHEC. Ground beefŚthe most common food source of STEC/EHEC strains Śis often contaminated during processing. Low bacterial numbers can transmit disease in humans, accounting for widespread infection from environmental sources and person-to-person spread. O157:H7 strains are the fourth most commonly reported cause of bacterial diarrhea in the United States (after Campylobacter, Salmonella, and Shigella spp.). STEC/EHEC characteristically causes grossly bloody diarrhea in more than 90% of cases. Significant abdominal pain and fecal leukocytes are common (70% of cases), but fever is not; absence of fever can incorrectly lead to consideration of noninfectious conditions (e.g., intussusception and inflammatory or ischemic bowel disease). STEC/EHEC disease is usually self-limited, lasting 5 to 10 days. HUS may develop in very young or elderly patients within 2 weeks of diarrhea. It is estimated that it occurs in 2% to 8% of cases of STEC/EHEC and that more than 50% of all cases of HUS in the United States and 90% of cases in children are caused by STEC/EHEC. Antibiotic therapy of STEC/EHEC cases of diarrhea should be avoided because antibiotics may increase the likelihood of developing HUS.
IV-88. The answer is E. (Chap. 150) Infections with Acinetobacter spp. are a growing cause of hospital-acquired infections worldwide. Surveillance data from Australia and Asia suggest that infections are common, and there are reports of community-acquired Acinetobacter infection. They typically infect patients receiving long-term care in intensive care units by causing ventilator-associated pneumonia, bloodstream infections, or urinary tract infections. They are particularly of concern because of their propensity to develop multidrug (or pan-drug) resistance and their ability to colonize units because of health care worker transmission. A. baumannii is the most common isolate and develops drug resistance avidly. Many strains are currently resistant to carbapenems (imipenem, meropenem). Last-line agents such as colistin, polymixin A, and tigecycline are often the only available therapeutic options. Tigecycline has been used for pneumonia caused by carbapenem-resistant strains but is not thought to be efficacious in bloodstream infection because usual dosing does not achieve therapeutic levels against Acinetobacter spp.
IV-89. The answer is B. (Chap. 151) Helicobacter pylori is thought to colonize about 50% (30% in
developed countries and >80% in developing countries) of the worldĺs population. The organism induces a direct tissue response in the stomach, with evidence of mononuclear and polymorphonuclear infiltrates in all of those with colonization regardless of whether or not symptoms are present. Gastric ulceration and adenocarcinoma of the stomach arise in association with this gastritis. MALT is specific to H. pylori infection and because of prolonged B-cell activation in the stomach. Although H. pylori does not directly infect the intestine, it does diminish somatostatin production, indirectly contributing to the development of duodenal ulcers. Gastroesophageal reflux disease is not caused by H. pylori colonization. Recent studies have demonstrated that colonization by some strains of H. pylori may be protective for the development of adeno-carcinoma of the esophagus and premalignant lesions such as Barrettĺs esophagus (odds ratio, 0.2ľ0.6).
IV-90. The answer is E. (Chap. 151) It is impossible to know whether the patientĺs continued dyspepsia is attributable to persistent Helicobacter pylori as a result of treatment failure or to some other cause. A quick noninvasive test to look for the presence of H. pylori is a urea breath test. This test can be done as an outpatient and gives a rapid, accurate response. Patients should not have received any proton pump inhibitors or antimicrobials in the meantime. Stool antigen test is another good option if urea breath testing is not available. If the urea breath test is positive more than 1 month after completion of first-line therapy, second-line therapy with a proton pump inhibitor, bismuth subsalicylate, tetracycline, and metronidazole may be indicated. If the urea breath test result is negative, the remaining symptoms are unlikely attributable to persistent H. pylori infection. Serology is useful only for diagnosing infection initially, but it can remain positive and therefore misleading in those who have cleared H. pylori. Endoscopy is a consideration to rule out ulcer or upper gastrointestinal malignancy but is generally preferred after two failed attempts to eradicate H. pylori. Figure IV-90 outlines the algorithm for management of H. pylori infection.