The patient has primary herpes simplex virus infection. Topical agents have no role in therapy, and intravenous therapy is reserved for patients who experience complications of primary human immunodeficiency virus (HIV) infection, such as pneumonitis, encephalitis, or hepatitis. The patient should receive some form of treatment because therapy partially relieves symptoms and accelerates healing. Newer antivirals are now available as alternatives to acyclovir. They include famciclovir, 250 mg orally three times daily or valacyclovir, 1 g orally twice daily for 7 days.

In primary syphilis rapid plasma reagin (RPR) test results are positive in only 70% of the patients. Thus, a negative RPR result does not rule out the diagnosis. The five options listed are part of the differential diagnosis for the syndrome of genital ulcers with regional adenopathy. In the United States, the three most common etiologies for genital ulceration and regional lymphadenopathy are herpes simplex virus (HSV), syphilis, and chancroid. Genital ulcers associated with HSV and chancroid (infection with Haemophilus ducreyi) generally present as multiple, painful ulcers. They generally have painful regional lymphadenopathy as well. Lymphogranuloma venereum (LGV) is an infection with Chlamydia trachomatis (typically serovars L1-3). LGV typically presents with a non-painful ulcer and tender lymphadenopathy or as a painful “buboe” formation (seen also with chancroid). From an epidemiologic standpoint, it is less common than primary syphilis and should be considered after consideration of primary syphilis. Granuloma inguinale is secondary to Klebsiella granulomatis infection and typically presents with a non-painful ulcer. These patients typically do not have lymphadenopathy, but may have painful “buboe.”

Objective: Identify and manage the Haemophilus ducreyi infection (a.k.a. chancroid).

The correct diagnosis is chancroid, an infection with Haemophilus ducreyi. Chancroid typically presents as a painful genital ulcer and tender regional lymphadenopathy. The ulcer usually has clearly demarcated borders and sometimes undermined. A
gray or yellow purulent exudate may be present over the ulcer, with a tendency to bleed when scraped. The inguinal lymphadenitis can sometimes liquefy and present as painful, fluctuant “buboes” that leak frank pus (as was seen in this patient). There is a high rate of co-infection with HIV.

One intramuscular dose of ceftriaxone is the recommended regimen. Azithromycin is another option, but a single dose is sufficient, rather than a 7-day course of therapy. Ciprofloxacin is effective but needs to be given twice daily for 3 days. Finally, erythromycin can be used at a dose of 500 mg orally four times daily for 7 days.

The Centers for Disease Control and Prevention (CDC) recommended offering testing to those who want to be tested, even if they are not symptomatic. The CDC also recently advocated the use of type-specific glycoprotein G-based serologic tests for the diagnosis of genital herpes in certain circumstances, particularly in suspected cases that are culture negative. A positive herpes simplex virus type 2 antibody test is indicative of an infection with anogenital herpes at some time in the past. The antibody test may be useful in the partner evaluation, although pretest counseling is important. The test is not recommended for routine screening in the population but should be made available to anyone requesting testing.

The patient has late-latent syphilis. This is evidenced by the fact that the patient has persistently positive nontreponemal tests, representing a previously infected patient without evidence of active disease. The recommended therapy is 3 weekly IM doses of benzathine penicillin G. In penicillin-allergic patients, doxycycline or tetracycline should be given for 4 weeks.

Doxycycline, not erythromycin, is the treatment of choice for secondary syphilis in penicillin-allergic patients. All the other statements are correct. The rash can manifest in many different ways, and by the time it is present, nontreponemal test results are positive almost 100% of the time, making the diagnosis relatively easy, if considered.

Many men and women with urethritis/mucopurulent cervicitis are minimally symptomatic or asymptomatic. Causative
agents include N. gonorrhoeae, Chlamydia trachomatis, herpes simplex virus, Trichomonas vaginalis, and Ureaplasma urealyticum. If a patient is unreliable, he should be treated empirically to help prevent further spread of the infection to other sexual partners.

The patient has gonorrhea. Gram stain is diagnostic, so there is no need to wait for the culture results. Due to the high prevalence of quinolone-resistant N. gonorrhoeae, empiric ciprofloxacin use is not appropriate. The lower dose of ceftriaxone is sufficient and empiric therapy for chlamydial infection should always be used concurrently with antigonococcal therapy.

Gram stain shows clue cells, which are characteristic of bacterial vaginosis. Trichomoniasis can also cause an increased vaginal pH, but does not demonstrate clue cells on the wetmount preparation. Neither of these findings is present in a vaginal yeast infections or chlamydial cervicitis.

The patient presents from community with a subacute, indolent illness and radiographic evidence of pneumonia. No mortality risk factors are present, and admission is probably not warranted. Piperacillin/tazobactam has no activity against common atypical bacterial organisms. Ciprofloxacin has poor activity against gram-positive organisms and should not be used in this setting. Correct therapeutic options include oral tetracyclines, macrolides, levofloxacin, gatifloxacin, or moxifloxacin. In this case, the hoarseness and partial response to clarithromycin raise suspicion for Chlamydia pneumoniae as a pathogen. Doxycycline is preferred in this setting.

The patient is acutely and severely ill with a community-acquired process. By IDSA guidelines, the appropriate therapy consists of a combination between a macrolide or fluoroquinolone and ceftriaxone, cefotaxime, or a β-lactam/β-lactamase inhibitor. Because he is HIV negative and acutely ill, trimethoprim-sulfamethoxazole would not provide adequate coverage for either atypical or serious gram-negative pathogens. Likewise, neither piperacillin-tazobactam nor the combination of clindamycin and ceftazidime would cover atypical pathogens. Intravenous doxycycline alone would not cover all likely typical bacterial pathogens. Of the provided answers, only the combination of azithromycin and ceftriaxone would treat severe pneumonia due to both Legionella and typical bacterial pathogens.

This patient presents with several clinical clues to the correct diagnosis. He presents with a nonproductive cough and low-grade fever, suggesting an atypical pathogen. His sputum Gram stain shows no predominant organism, despite a fulminant process. He has evidence of hemolytic anemia and cardiac dysfunction, illustrating the potentially severe complications of an ordinarily indolent pathogen.

Several factors can contribute to initial antibiotic therapy failure in community-acquired pneumonia. First, one should consider the correctness of the diagnosis. A number of diagnoses may lead to pulmonary infiltrates, including noninfectious diseases such as heart failure. Host factors such as empyema, immunodeficiency, and bronchial tree obstruction may slow the response to antibiotics. It is also important to consider difficulties with the regimen itself: Is this the wrong drug or dose? Is the patient adhering to the regimen? The clinician must also place less common microbial pathogens in the differential diagnosis, as some pathogens do not respond to standard antibiotic regimens. Finally, certain pathogens, such as Legionella species and Streptococcus pneumoniae, may cause overwhelming infection that may not immediately respond to antibiotics.

In this circumstance, the patient is immunocompromised by virtue of his lymphoma. He has a pet parakeet and might have pneumonia caused by an unusual pathogen, such as Chlamydophila psittaci. He has a grandchild with a respiratory illness, but it is January, raising the question of viral pathogens such as influenza, respiratory syncytial virus, adenovirus, parainfluenza virus, and others. Given his rapid decline, bronchoscopy is likely indicated to obtain a specimen for staining and culture for a broad range of pathogens. Serology may be useful to help diagnose infection with Chlamydia species or other atypical pathogens, such as Legionella and Mycoplasma species.

This patient, who is seemingly recovering from acute influenza A, suffers a relapse of symptoms with a more acute presentation. The primary concern is for a bacterial superinfection in the lungs. Staphylococcus aureus and Streptococcus pneumoniae are important pathogens in this setting; community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a concern in this toxic-appearing patient. Blood and sputum studies are clearly indicated to identify a pathogen and direct therapy. Intravenous vancomycin and linezolid are therapeutic options for CA-MRSA. Given the clinical course and radiographic change, it is unlikely that a change in antiviral therapy will have an effect on the patient’s course.

Therapy with TNF inhibitors such as infliximab has been associated with reactivation of tuberculosis and endemic mycoses such as histoplasmosis. In this setting, protein purified derivative skin testing, Histoplasma urinary antigen testing, and fungal serology battery are clearly indicated. Because skin and serologic testing can yield delayed or no diagnosis, bronchoscopy can be critical to obtain diagnostic specimens and direct antimicrobial therapy. The patient’s subacute illness and the radiographic pattern are less consistent with “typical” bacterial pathogens such as Streptococcus pneumoniae, and pneumococcal urinary antigen testing is not indicated for this patient.

If acute infectious diarrhea can be linked to the ingestion of a certain meal (for example in a family outbreak setting), the incubation period can be helpful for diagnosis. Staphylococcus aureus and Bacillus cereus have incubation periods of less than 6 hours, Clostridium perfringens and B. cereus between 6 and 24 hours, noroviruses, enterotoxigenic Escherichia coli, Vibrio, Salmonella, Shigella, Campylobacter, Yersinia, Giardia, Cyclospora, Cryptosporidium between 16 and 72 hours, respectively. Certain foods are also linked to particular infections: undercooked poultry to campylobacteriosis, undercooked hamburger to shiga toxin-producing E. coli (STEC), seafood to Vibrio species, improperly refrigerated fried rice to B. cereus, fresh soft cheeses to Listeria monocytogenes, contaminated eggs to Salmonella species, unrefrigerated potato salad to Staphylococcus aureus (preformed enterotoxin), and undercooked pork to Yersinia enterocolitica.

The most likely cause in this patient is a viral infection. Because the illness is less than 24 hours in duration and is not associated with inflammatory features, the detection of fecal leukocytes and stool cultures are not indicated at this time. Rotavirus polymerase chain reaction should not be used in routine clinical care. Oral rehydration is the appropriate management here. Antimotility agents such as loperamide and diphenoxylate may be used here if needed because the diarrhea is not bloody. Empiric antimicrobials are indicated for moderate to severe travelers’ diarrhea, and febrile, community-acquired, inflammatory diarrhea, particularly in immunocompromised patients, unless STEC is suspected on epidemiologic grounds. Severe nosocomial
diarrhea in patients receiving systemic antibiotics or chemotherapeutic agents should also be treated empirically with metronidazole, pending the results of a Clostridium difficile toxin assay. Persistent diarrhea for more than 10 days should raise the concern of protozoal pathogens, such as Giardia and Cryptosporidium; empiric therapy with metronidazole, pending stool microscopy or immunoassay, is reasonable in this setting.

The microbiology of acute uncomplicated cystitis in women is predictable, so empiric antimicrobial therapy would be appropriate. Collecting urine for culture should be considered if empiric therapy fails. Ultrasound of the urinary bladder may be useful in cases with persistent symptoms to rule out the presence of a stone or diverticulum. Renal ultrasound should be considered if a clinical suspicion for upper UTI is present. First-line treatment for uncomplicated cystitis includes TMP-SMX for 3 days. Extending therapy for 7 days may be considered in patients with persistent symptoms. Other agents that are commonly used in the United States are nitrofurantoin (100 mg twice daily for 5 days) and fosfomycin (3 g in a single dose). Fluoroquinolones and β-lactams are generally efficacious agents, but the most recent Infectious Disease Society of America (IDSA) guidelines recommend against using them as first-line agents given their higher rates of adverse events. The use of vaginal spermicides is a known risk factor for UTI; women with recurrent UTI should be advised to use another form of contraception. Once the diagnosis is established, antimicrobial self-treatment at the onset of dysuria and postcoital prophylaxis are reasonable options for this young woman with recurrent cystitis.

In the appropriate setting, patients presenting with a mononucleosis-type illness should be questioned about their sexual practices because the acute retroviral syndrome has a similar presentation. HIV antibody test is usually negative during the acute illness and may require several weeks or months to become positive. An accurate diagnosis requires a plasma HIV RNA test or HIV p24 antigen detection. This has clear clinical and public health implications because a large proportion of HIV-infected people are not aware of their HIV status; thus, they may present at a later stage of disease, while continuing to transmit the infection to others. The CDC currently recommends the “opt-out” HIV screening approach, where assent is inferred unless the patient declines testing. The statement in (b) refers to a patient with influenza, an illness that, unlike infectious mononucleosis, may be preventable with a vaccine and is treatable with specific antiviral agents. The statement in (c) refers to a patient with acute sinusitis, which is not associated with splenomegaly or generalized lymphadenopathy. The statement in (d) refers to a patient with “strep throat,” a form of pharyngitis more common in children than adults and associated with certain clinical features that do not include splenomegaly or generalized lymphadenopathy. The statement in (e) could apply to a patient with nonspecific upper respiratory tract infection (common cold) or bronchitis; these illnesses are gradual in onset and, again, not associated with splenomegaly or generalized lymphadenopathy.

Risk factors for a soft tissue infection in this woman include the diabetes and varicose veins. The portal of entry for the causative organism is likely the erosion overlying her tibia. The ill-defined redness is more consistent with cellulitis than erysipelas. It is true that blood cultures are usually not positive in most cases of cellulitis, but treatment with penicillin would only be appropriate for erysipelas. Herpes simplex virus infection is not a consideration here, and sexual activity is not a risk factor for cellulitis. Even though one might consider admission to the hospital to initiate intravenous antimicrobial therapy and observe clinical improvement, surgical consultation would only be warranted for this case if necrotizing fasciitis is clinically or radiologically suspected. Topical antifungal therapy may be considered here only if tinea pedis is present.

Babesiosis is a protozoal infection with the genus Babesia, leading to a wide range of clinical manifestations, from asymptomatic to severely ill, often depending on the immune status of the host. Babesia directly infects red blood cells (RBCs), where it undergoes asexual reproduction, forming the characteristic tetrad (maltese cross appearance). Risk factors for severe illness include the following: age >50, splenectomy, immunosuppression, TNF-α inhibitor use, and co-infection with HIV. Typically, immunocompetent patients have mild non-specific symptoms, with high fever (up to 40°C) being the hallmark of the disease. Other constitutional symptoms, such as malaise, fatigue, and headache, may be seen. On examination, there can be some mild hepatosplenomegaly, but lymphadenopathy and signs of liver failure are rare. Patients with the above risk factors are prone to a more severe disease, which can manifest as acute respiratory distress syndrome (ARDS), disseminated intravascular coagulopathy (DIC), congestive heart failure, renal failure, and splenic infarcts.

The other conditions listed can often present with similar symptoms. Ehrlichiosis infects granulocytes and monocytes. Histoplasmosis is typically seen in the Ohio River Valley and may be phagocytized by monocytes and granulocytes, but typically does not cause infection of RBCs. Borrelia and trypanosomes may be observed in peripheral blood smears as extracellular organisms, but do not infect RBCs.

This man most likely has gonorrhea. First-generation cephalosporins and long-acting penicillins have no place in the treatment of gonorrhea. Ceftriaxone or ciprofloxacin alone would be inadequate because there is a high incidence of chlamydial infections in patients with gonorrhea. Dual antimicrobial coverage is therefore necessary. Azithromycin is no longer considered appropriate monotherapy as high rates of macrolide resistance have been encountered in the treatment of gonorrhea.

Immunocompromised individuals are particularly susceptible to symptomatic herpes zoster, which can result in Ramsay Hunt syndrome. Pain and vesicles appear in the external auditory canal, and there may be loss of taste sensation in the anterior two-thirds of the tongue. The geniculate ganglion of the sensory branch of the facial nerve is involved.