Norovirus is the most common cause of foodborne outbreaks, followed by Salmonella.

The most common causes of dysentery (grossly bloody stools) in descending frequency are Shigella, Campylobacter, nontyphoid Salmonella, and Shiga toxin-producing Escherichia coli (STEC).

Indications for stool culture and assay to detect STEC include passage of ≥6 unformed stools/day, persistent diarrhea for ≥1 week, fever, dysentery, and outbreak settings.

The diagnosis depends on the incubation period, epidemiologic, and clinical clues.

Rehydration is the most important measure in the management of acute infectious diarrhea (AID).

A diet of easily digestible food is generally recommended.

Although many cases of bacterial diarrhea may resolve without a specific antimicrobial therapy, several patient groups who are at risk of systemic complications should receive antimicrobial therapy; the choice of which one depends on the causative pathogen.

Rifaximin or bismuth subsalicylate reduces the risk of traveler’s diarrhea by about 70%.

Women are at a higher risk for urinary tract infection (UTI) than men. Up to 50% of women have recurrent UTI within 2 years of an initial episode.

Escherichia coli is the most common causative organism.

Typical symptoms are sufficient for the diagnosis of acute cystitis, and urinalysis may aid in patients with atypical presentations.

Routine urine culture is indicated before initiating the treatment for pyelonephritis, complicated UTI, catheter-associated UTI, or prostatitis, but not for a simple cystitis.

Nitrofurantoin, trimethoprim/sulfamethoxazole (TMPSMX), TMP, and fosfomycin are the first-line antibiotics for simple cystitis, and TMP-SMX or a quinolone for acute pyelonephritis or prostatitis. Antimicrobial therapy for complicated UTI and catheter-associated UTI should be directed by culture results.

Screening for and treatment of asymptomatic bacteriuria is indicated in early pregnancy and before urologic procedures in which mucosal bleeding is anticipated.

Options for recurrent cystitis in women are continuous prophylaxis, postcoital prophylaxis, or self-initiated therapy.

Topical intravaginal estriol cream in postmenopausal women reduces recurrent UTIs.

Symptoms such as production of yellow sputum, sore throat, fever, and colored nasal discharge have poor predictive evidence for the efficacy of the prescribed antibiotics.

A maculopapular rash is noted on presentation in 5% to 10% of infectious mononucleosis cases due to Epstein-Barr virus (EBV), and in up to 95% of patients who receive ampicillin or amoxicillin for presumed group A streptococci (GAS) pharyngitis.

In patients with mononucleosis due to EBV, lymphocytosis and large, lobulated “atypical” lymphocytes are often seen on peripheral blood smears (sensitivity 75% and specificity 92%).

Treatment of infectious mononucleosis is supportive; antiviral agents are not recommended.

Although GAS causes only 10% of pharyngitis cases in adults, about 70% of those presenting with sore throat to primary care physicians receive antibiotics.

At least 10% of the pharyngitis cases in people aged 15 to 24 years are due to Fusobacterium necrophorum.

The clinical diagnosis of GAS pharyngitis is not reliable. Thus, throat swab for streptococcal rapid antigen detection test (RADT) using chemiluminescent deoxyribonucleic acid (DNA) probes should be done to guide the antimicrobial therapy (sensitivity 70% to 90% and specificity 95%). A negative RADT should be backed by the culture (90% to 95% sensitive).

Oral penicillin or amoxicillin for 10 days remains the treatment of choice for GAS pharyngitis. Alternatives include intramuscular benzathine penicillin, oral first-generation
cephalosporins, oral macrolides, or oral clindamycin. Tetracyclines, sulfonamides, and fluoroquinolones, particularly ciprofloxacin, are not recommended.

Tonsillectomy to reduce the frequency of GAS pharyngitis is not recommended in adults.

Majority (90% to 98%) of acute sinusitis cases are due to viruses, with only about 2% to 10% caused by bacteria (Streptococcus pneumoniae 38%, Haemophilus influenzae 36%, Moraxella catarrhalis 16%, Staphylococcus aureus 13%, and Streptococcus pyogenes 4%).

Purulent nasal drainage and facial pain are the cardinal features of acute sinusitis. Clinical scenarios suggestive of acute bacterial sinusitis include persistence of symptoms without improvement for ≥10 days, severe symptoms (such as fever ≥102°F) lasting 3 to 4 days, or initial improvement followed by a later worsening of symptoms.

Majority of patients with acute sinusitis do not require imaging studies, culture confirmation by sinus endoscopy, or sinus aspiration. Nasal cultures are not representative.

Most cases of mild sinusitis improve with topical intranasal steroids and topical or systemic nasal decongestants, without antimicrobial therapy. For patients with features suggestive of acute bacterial rhinosinusitis, amoxicillin—clavulanic acid for 5 to 7 days is the first-line agent, with doxycycline as an alternative choice. Respiratory fluoroquinolones or a combination of an oral third-generation cephalosporin are second-line agents. High doses of amoxicillin—clavulanic are recommended for certain populations. Macrolides, TMP—SMX, and second- or third-generation cephalosporins monotherapy are not recommended.

Most cases of acute bronchitis are due to viruses. Symptoms last 3 weeks. Treatment is symptomatic.

Patients with influenza typically present with sudden diffuse or throbbing headache, high fever, severe myalgia, and dry cough.

Rapid “point of care” influenza tests can rule in, but not rule out the diagnosis. Thus, it should be backed up by a more sensitive PCR test.

Neuraminidase inhibitors, oseltamivir and zanamivir, shorten the duration of influenza illness by 1 to 2 days, prevent hospitalizations, secondary complications, and death.

Health-care facilities should track influenza vaccination of health-care workers.

Purulent cellulitis is mostly due to methicillin-resistant Staphylococcus aureus (MRSA) 59% and methicillinsusceptible Staphylococcus aureus (MSSA) 17%, while diffuse, nonpurulent/nonculturable cellulitis is mostly due to GAS (70%) and MSSA.

Empiric oral antimicrobial choices for purulent cellulitis include clindamycin, TMP-SMX, tetracycline, or linezolid, and for nonpurulent cellulitis, dicloxacillin, or cephalexin.

Almost all cases of erysipelas are due to GAS. Penicillin is the treatment of choice.

Most infected bite wounds are polymicrobial. Treat with amoxicillin-clavulanic acid.

In contrast to paronychia or felon treatment, incision and drainage are contraindicated for herpetic whitlow because this may result in viremia or a secondary bacterial infection.

Antifungal therapy for onychomycosis takes several weeks, so microbiologic documentation is required.