Giardiasis

Giardiasis is caused by the flagellated protozoan Giardia lamblia (duodenalis), transmitted via the fecal-oral route through contaminated water (including recreational water and, notably, mountain streams, giving it the colloquial name "beaver fever" in some regions) or food, with cysts being the infective, environmentally resistant form. It is one of the most common causes of parasitic diarrhea worldwide and a frequent cause of traveler's diarrhea.

Acute infection causes foul-smelling, greasy, non-bloody diarrhea (reflecting malabsorption from the parasite's attachment to and disruption of the duodenal/jejunal brush border), bloating, flatulence, abdominal cramping, and nausea, typically beginning 1 to 3 weeks after exposure. A subset develop chronic infection, with intermittent or persistent symptoms, weight loss, and, occasionally, secondary lactose intolerance from brush border disruption.

Stool antigen testing (EIA) or PCR offers good sensitivity and is preferred over microscopy alone
Stool microscopy for cysts/trophozoites has lower sensitivity given intermittent shedding; testing of 3 separate stool samples over different days improves yield if microscopy alone is used
Duodenal aspirate or biopsy is reserved for cases with high clinical suspicion and repeatedly negative stool testing

Metronidazole 250 to 500 mg PO tds for 5 to 7 days, or tinidazole 2 g PO as a single dose (higher cure rate and better tolerated single-dose option where available)
Alternatives: nitazoxanide 500 mg PO bd for 3 days (useful where metronidazole is not tolerated or in young children given a convenient suspension formulation)
Avoid alcohol during and after metronidazole/tinidazole as per standard nitroimidazole precautions
Secondary lactose intolerance may persist for weeks after successful treatment and should be considered in ongoing symptoms post-eradication, managed with temporary dietary lactose restriction
Treatment failure (roughly 10 to 20% with a single course) is managed with a repeat or extended course, or a different agent class

Referral: gastroenterology/infectious disease for refractory or recurrent infection.

Gonococcal Arthritis

Gonococcal arthritis is a manifestation of disseminated gonococcal infection (DGI), occurring when Neisseria gonorrhoeae spreads hematogenously from a mucosal site (genital, rectal, or pharyngeal) to distant sites, most commonly joints and skin.

It remains the most common cause of septic arthritis in sexually active young adults in many settings, and disproportionately affects women, in whom the primary mucosal infection is more often asymptomatic and therefore untreated before dissemination occurs.

DGI classically presents in one of two overlapping patterns. The arthritis-dermatitis syndrome (more common) features fever, migratory polyarthralgia, tenosynovitis (particularly of the wrists, fingers, ankles, and toes, a relatively distinctive feature), and a sparse pustular or vesiculopustular rash on an erythematous base, typically on the distal extremities and trunk. The purulent arthritis syndrome features a true septic monoarthritis or oligoarthritis, most commonly affecting the knee, wrist, or ankle, without the preceding migratory or dermatologic features, and mimics other causes of septic arthritis clinically.

Blood cultures are positive in a minority of cases (particularly the arthritis-dermatitis pattern), but should always be sent
Synovial fluid analysis and culture (from the purulent arthritis pattern) has low culture sensitivity for gonococcus specifically, given its fastidious growth requirements; NAAT of synovial fluid, where available, offers substantially higher sensitivity
NAAT testing of all mucosal sites (urethral/vaginal, rectal, pharyngeal) regardless of symptoms is essential, since this is often where the organism is most reliably detected, even when disseminated cultures and joint fluid are negative
Skin lesion Gram stain and culture, if pustules are present
Synovial fluid should still be sent for standard cell count, Gram stain, and culture as for any suspected septic arthritis (see that entry), given the differential includes other bacterial causes

Ceftriaxone 1 g IV/IM once daily, continued for 24 to 48 hours after clinical improvement begins, then stepped down to an oral agent (guided by susceptibility if available, otherwise cefixime 400 mg PO bd, or per local resistance patterns) to complete a total treatment course of 7 days
Given the frequency of chlamydial coinfection, add doxycycline 100 mg PO bd for 7 days empirically unless chlamydia has been specifically excluded
Purulent arthritis with a significant joint effusion may require joint aspiration or surgical drainage in addition to antibiotics, following the same principles as any septic arthritis (see that entry)
Sexual partners in the preceding 60 days should be tested and treated
Follow local antimicrobial resistance guidance closely given rising, regionally variable gonococcal resistance

Referral: rheumatology or orthopedics for joint aspiration/drainage where indicated; sexual health services for partner notification and full STI screening.

Giardiasis

Overview

Clinical Features

Diagnosis

Management

Overview

Clinical Features

Diagnosis

Management