01Approach to the Critical Patient/attcp44

Immediate priorities

›Life-threatening presentations

›Severe dehydration and shock

›SBP < 90 mmHg

›MAP < 65 mmHg

›Tachycardia with hypotension

›Profuse watery diarrhea in immunocompromised host

›Stool output exceeding 10 L/day possible in CD4 < 100 cells/mm3

›Cholera-like syndrome with rapid fluid depletion

›Altered mental status

›Encephalopathy from hyponatremia or severe dehydration

›Sepsis-associated brain dysfunction

›If haemodynamic compromise, initiate IV resuscitation immediately

›Isotonic crystalloid bolus 20 to 30 mL/kg

›Reassess every 15 to 30 minutes

Monitoring and targets

›Resuscitation targets

›Urine output >= 0.5 mL/kg/hour

›Foley catheter for accurate monitoring in severe cases

›Oliguria as marker of inadequate resuscitation

›Heart rate < 100 beats/min

›Tachycardia persisting with fluid resuscitation suggests ongoing losses

›Electrolyte normalisation

›Potassium target 3.5 to 5.0 mmol/L

›Sodium target 135 to 145 mmol/L

›Escalation triggers

›Worsening mental status despite resuscitation

›ICU-level care

02History/hx87

Presentation pattern

›Core diarrheal syndrome

›Profuse watery non-bloody diarrhea

›Median 12 stools per day in outbreak settings

›Non-bloody pattern distinguishes from invasive bacterial enteritis

›Crampy lower abdominal pain

›Diffuse periumbilical location

›Colicky character

›Nausea and vomiting

›Variable severity

›Limits oral rehydration

›Fever

›Present in approximately one-third of cases

›High fever uncommon; suggests bacterial co-infection

Temporal and exposure history

›Incubation and duration

›Incubation period 7 to 10 days with range 2 to 14 days

›Symptom onset clue for tracing exposure

›Duration 2 to 3 weeks in immunocompetent hosts

›Relapse after apparent resolution is common

›Persistence beyond 4 weeks in immunocompetent host warrants workup

›Exposure history

›Recreational water exposure

›Swimming pools and water parks

›Lakes and rivers

›Oocysts resist standard chlorination

›Contaminated drinking water

›Outbreak investigation trigger

›Nationally notifiable condition in the United States

›Animal contact

›Pre-weaned calves

›Dairy farming occupational exposure

›Person-to-person transmission

›Daycare attendance or employment

›Household contacts with similar symptoms

›Sexual history

›Men who have sex with men at elevated risk via fecal-oral route

›Travel history

›Countries with less stringent water treatment

›Imported food exposure

Alarm features and red flags

›Features requiring urgent assessment

›Immunocompromised state with persistent or worsening diarrhea

›HIV with unknown or low CD4

›Organ transplant or chemotherapy

›Biliary symptoms

›Right upper quadrant pain

›Jaundice

›Fever with elevated liver enzymes

›Respiratory symptoms

›Cough or dyspnea

›Pulmonary cryptosporidiosis may be under-recognised

›Significant weight loss

›Failure to thrive in children

›Cachexia in adult HIV patients

›Bloody diarrhea

›Suggests alternative or co-diagnosis

›Invasive bacterial enteritis, CMV colitis consideration

Risk factors

›Host immunosuppression

›HIV/AIDS with CD4 < 100 cells/mm3 highest risk for severe disease

›Life-threatening cholera-like syndrome possible

›Biliary and pulmonary involvement risk

›Organ transplant recipients

›T-cell immunosuppressive regimens

›Tacrolimus and cyclosporine

›Primary immunodeficiencies

›MHC class II deficiency

›CD40 ligand deficiency

›Hyper-IgM syndrome

›Population risk

›Children under 5 years at highest risk globally

›Daycare and institutional transmission

›Nutritional impact on growth when acquired in infancy

›International travellers to endemic regions

Past medical history and medications

›Relevant conditions

›Prior cryptosporidiosis episodes

›Recurrence common

›Assess ART optimisation in HIV patients

›Chronic GI conditions

›IBD may confound presentation

›IBS overlap

›Malnutrition

›Worsens outcomes especially in children

›Medication review

›Current ART regimen and adherence in HIV patients

›Determine CD4 trend and viral load

›Immunosuppressants

›Dose and class of therapy

›Antidiarrheal use prior to presentation

›Loperamide or other agents

03Physical Exam/exam52

Vital signs and general assessment

›Haemodynamic status

›Blood pressure

›Hypotension SBP < 90 mmHg as critical finding

›Orthostatic blood pressure change

›Heart rate

›Tachycardia > 100 beats/min indicates dehydration severity

›Temperature

›Fever in approximately one-third of cases

›High fever suggests bacterial superinfection

›Respiratory rate

›Tachypnoea with severe metabolic acidosis

›Respiratory symptom with pulmonary involvement

›General appearance

›Degree of dehydration

›Sunken eyes

›Dry mucous membranes

›Decreased skin turgor

›Wasting and cachexia in chronic immunocompromised cases

Abdominal exam

›Abdominal findings

›Diffuse tenderness

›Periumbilical location typical

›Non-peritoneal pattern

›Hyperactive bowel sounds

›Profuse watery diarrhea correlation

›Right upper quadrant tenderness

›Biliary tract involvement

04Differential Diagnosis/ddx61

Life-threatening mimics

›Serious differential diagnoses

›Cholera

›Watery diarrhea with rice water stools

›Rapid severe dehydration in endemic areas

›ICD-10 A00.9

›Clostridium difficile colitis

›Antibiotic exposure history key

›Toxin assay distinguishes

›ICD-10 A04.7

›CMV colitis in HIV patients

›Advanced HIV with CD4 < 50 cells/mm3

›Bloody diarrhea more common

›Colonoscopy with biopsy required

›ICD-10 B25.1

Common infectious mimics

›Other protozoan and parasitic infections

›Giardiasis

›Watery diarrhea with bloating and flatulence

›More chronic and intermittent than cryptosporidiosis

›Stool antigen or NAAT confirms

›ICD-10 A07.1

›Cyclosporiasis

›Imported produce exposure

›Responds to trimethoprim-sulfamethoxazole

›ICD-10 A07.4

›Cystoisosporiasis

›Immunocompromised host predominantly

05Laboratory Tests/lt56

Stool diagnostic testing

›Specific Cryptosporidium testing required

›Not included in routine ova and parasite examination

›Must specifically request Cryptosporidium testing

›Clinical communication critical

›Multiplex molecular panel NAAT/PCR

›Becoming standard of care

›Sensitivity approximately 97%

›Specificity approximately 98%

›Detects Cryptosporidium alongside other enteric pathogens

›Direct fluorescent antibody DFA

›Sensitivity and specificity 99.8 to 100%

›Reference standard method

›Preferred confirmatory test

›Stool antigen enzyme immunoassay

›Sensitivity 66 to 100% with variable performance

›Some rapid immunochromatographic tests have poor specificity

›Modified acid-fast stain

›Approximately 70% sensitivity

›Lower than molecular methods

›Oocysts stain red on blue-green background

Electrolytes and metabolic panel

›Basic and comprehensive metabolic panel

›Electrolytes

›Hyponatremia from profuse diarrhea and fluid shifts

›Hypokalemia from GI losses

›Metabolic acidosis from volume loss and bicarbonate depletion

›Renal function

06Diagnostic Tests/dt59

Scoring Systems

›Severity stratification framework

›Immune status based severity classification

›Immunocompetent mild: watery diarrhea 1 to 2 weeks, self-limited

›Immunocompetent persistent: symptoms > 2 weeks, consider nitazoxanide

›HIV CD4 > 200: transient or mild, usually self-limited with ART

›HIV CD4 100 to 200: chronic relapsing, improves with ART

›HIV CD4 < 100: profuse cholera-like diarrhea, life-threatening without ART

›Dehydration severity scoring

›Mild: thirst, normal vitals, adequate urine output

›Moderate: tachycardia, orthostatic changes, reduced urine output

›Severe: hypotension, oliguria, altered mental status

›Limitations of scoring

›No validated cryptosporidiosis-specific severity score in clinical use

›CD4 count is the primary prognostic determinant

›Clinical trajectory supersedes any single parameter

MRI

›MRI role in cryptosporidiosis

›Not routinely indicated for intestinal disease

›CT and ultrasound are preferred modalities

›Availability and time constraints in acute setting

›Magnetic resonance cholangiopancreatography MRCP

›Non-invasive biliary tree evaluation

›Primary sclerosing cholangitis pattern characterisation

›Useful when ERCP is high risk or unavailable

›MRI abdomen for complex hepatobiliary disease

›Liver parenchymal assessment

›Biliary ductal anatomy before intervention

07Disposition/dispo51

Discharge criteria

›Outpatient management appropriate

›Immunocompetent patients meeting all criteria

›Tolerating oral fluids adequately

›Stable vital signs without orthostasis

›Adequate urine output

›Electrolytes within acceptable range

›Reliable follow-up and return precautions understood

›Mild dehydration correctable with oral rehydration therapy

›No ongoing signs of haemodynamic compromise

›No high-risk features present

›Not immunocompromised

›No biliary involvement signs

Admission criteria

›Indications for inpatient management

›Dehydration severity

›Moderate to severe dehydration not responding to oral rehydration

›Inability to tolerate oral intake

›Ongoing large volume losses exceeding oral replacement capacity

›Haemodynamic instability

›Hypotension or orthostasis

›Tachycardia not resolving with fluid challenge

›Electrolyte abnormalities

›Significant hyponatremia, hypokalemia, or acidosis requiring IV correction

›Immunocompromised host with profuse diarrhea

›Stool volumes can exceed 10 L per day

›Rapid deterioration risk

›Biliary tract involvement

08Treatment/t72

Fluid resuscitation and supportive care

›Rehydration strategy

›Oral rehydration therapy for mild to moderate dehydration

›Oral rehydration solution ORS preferred

›WHO ORS formulation: glucose 75 mmol/L, sodium 75 mmol/L

›Avoid dairy during acute illness

›Secondary lactase deficiency risk

›Intravenous fluid therapy for moderate to severe dehydration

›Normal saline or Ringer's lactate bolus 20 to 30 mL/kg

›Reassess after each bolus

›Add potassium once urine output established

›Electrolyte replacement

›IV potassium chloride for hypokalemia

›Sodium correction for hyponatremia

›Nutritional support

›Enteral nutrition preferred over parenteral

›Small frequent meals during recovery

›Avoid dairy products during acute illness

›Total parenteral nutrition rarely indicated

›Reserve for inability to use GI tract

›Long-term nutritional monitoring in children

›Growth assessment at follow-up visits

Antiparasitic therapy in immunocompetent patients

›Nitazoxanide

›FDA-approved for cryptosporidiosis in immunocompetent patients

›Take with food to improve absorption

›Not shown effective in HIV-infected patients when used alone

›Adult and adolescent dosing (>= 12 years)

›500 mg PO BID with food for 3 days

›Children 4 to 11 years

›200 mg PO BID for 3 days using oral suspension

›Children 1 to 3 years

›100 mg PO BID for 3 days using oral suspension

›Indication threshold

›Symptoms persisting beyond 2 weeks in immunocompetent host

›Consider earlier in symptomatic patients with significant illness burden

Treatment in HIV and immunocompromised patients

›Antiretroviral therapy as primary treatment

›ART initiation or optimisation is the mainstay of treatment

›Immune reconstitution to CD4 > 100 cells/mm3 leads to resolution

›ART alone may resolve cryptosporidiosis with immune recovery

›Never delay or omit ART in favour of antiparasitic agents alone

›ID specialist guidance for ART selection

›Drug interactions with antiparasitics

›Viral load and resistance testing

›Nitazoxanide in HIV patients

›500 to 1000 mg PO BID with food for minimum 14 days

›Longer course required compared with immunocompetent patients

›Always used in combination with ART not instead of

›Paromomycin

›Alternative for HIV patients

›500 mg PO QID for 14 to 21 days plus ART

›Non-absorbed aminoglycoside with luminal activity

›Limited systemic absorption

›Combination with azithromycin has been used in refractory cases

›Biliary tract disease management

›ERCP for diagnosis and therapeutic intervention

›Sphincterotomy

›Stenting for biliary obstruction

›ART optimisation essential for biliary disease

›Immune reconstitution required for durable response

Symptom control and adjuncts

›Antimotility agents

›Loperamide for symptomatic relief

›4 mg PO initially then 2 mg after each loose stool

›Maximum 16 mg per day

›Use with caution in inflammatory or invasive diarrhea

›Tincture of opium

›May be more effective than loperamide in profuse diarrhea

›Reserved for severe symptoms

›Octreotide not recommended

›No more effective than oral antidiarrheals in studies

›Zinc supplementation in children

›20 mg per day for 10 to 14 days in children over 6 months

›Reduces duration and severity of diarrheal illness

›WHO guideline recommendation for acute diarrhea in children

09Special Populations/sp56

Pregnancy

›Pregnancy-specific considerations

›Risk profile

›Cryptosporidiosis generally self-limited in immunocompetent pregnant women

›Severe dehydration poses risk of preterm labour and fetal compromise

›Foetal monitoring when dehydration is significant in viable gestation

›Treatment limitations

›Nitazoxanide safety in pregnancy not established

›Category B classification but limited human data

›Weigh risk-benefit; supportive care preferred in mild cases

›Paromomycin considered safer alternative due to minimal systemic absorption

›Rehydration priority

›Aggressive oral and IV rehydration

›Maintain uterine perfusion

›Electrolyte monitoring and correction

›Foodborne and waterborne precautions

›Avoid recreational water activities during outbreaks

›Boil or filter drinking water if municipal supply safety uncertain

Geriatric

›Older adult considerations

›Atypical presentation risk

›Delirium may precede GI symptoms

›Fever may be blunted or absent

›Falls from orthostasis and dehydration

›Higher dehydration risk

›Reduced thirst sensation

›Decreased physiologic reserve

›Polypharmacy with diuretic use

10Background/b70

Epidemiology

›Global burden

›Cryptosporidiosis is a major cause of diarrheal morbidity and mortality globally

›Lancet Infectious Diseases 2015 systematic review highlights burden in low-income countries

›Leading cause of diarrheal mortality in children in sub-Saharan Africa and South Asia

›United States epidemiology

›Nationally notifiable condition

›Leading cause of recreational water illness outbreaks in the US

›Reported cases vary seasonally with water recreation peaks in summer

›High-risk groups

›HIV/AIDS patients historically had the highest mortality before ART era

›Children under 5 years globally highest burden

›Immunocompromised hosts including transplant and chemotherapy patients

›Species distribution

›C hominis predominantly human-to-human transmission

›C parvum zoonotic transmission from cattle predominant in rural and occupational settings

›Other species account for minority of cases

›Climate sensitivity

›Waterborne disease sensitive to climate variability

›Increased heavy rainfall events associated with contamination of water sources

Pathophysiology

›Parasite and lifecycle

›Cryptosporidium is an apicomplexan protozoan parasite

›Oocysts are the environmentally resistant transmission form

›Infectious dose as low as 10 to 100 oocysts

›Oocysts resist standard chlorination at typical pool concentrations

›Inactivated by UV disinfection and high chlorine doses

›Infection cycle

›Ingested oocysts excyst in small intestine

›Sporozoites invade enterocytes at brush border

›Intracellular but extracytoplasmic location protects from immune clearance

›Asexual and sexual replication cycles within host

›Oocysts shed in stool beginning within 5 to 7 days of infection

›Disease mechanisms

›Intestinal epithelial disruption

›Villous atrophy and crypt hyperplasia

›Increased intestinal permeability

›Malabsorptive and secretory diarrhea

›Immune evasion

›T-cell mediated immunity is the primary defence

›CD4 count drives severity in HIV infection

›Primary immunodeficiencies affecting T-cell function increase susceptibility

›Biliary and extra-intestinal disease

›Biliary epithelium invasion causing cholangitis

›Sclerosing cholangitis pattern in advanced HIV

›Pulmonary involvement via ingestion or aspiration of contaminated water

›Pancreatic involvement described

Therapeutic Considerations

›Treatment principles

›Immune status determines treatment strategy

›Supportive care is appropriate first-line for immunocompetent patients

›ART is non-negotiable in HIV-infected patients

›No antiparasitic has demonstrated reliable efficacy without immune reconstitution

›Nitazoxanide mechanism

›Inhibits pyruvate-ferredoxin oxidoreductase enzyme pathway

›Active against Cryptosporidium parvum in vitro and in immunocompetent patients

›Limited activity in severely immunocompromised hosts without immune recovery

›Paromomycin mechanism

›Non-absorbed aminoglycoside acting luminally

›Inhibits ribosomal protein synthesis

›Used as adjunct to ART in refractory HIV cases

›Future and investigational therapies

›Bumped kinase inhibitors and nitazoxanide analogues in development

›Paediatric-specific formulations lacking globally

›NITAX trial investigating nitazoxanide in HIV-infected adults with cryptosporidiosis

›Prevention strategies

›Water treatment improvements

›Pool hygiene and exclusion policies

›No approved vaccine currently available

›Antibiotic stewardship note

›Empiric antibiotics should not be used for watery diarrhea without identified cause

›Risk of C difficile induction

›Does not cover Cryptosporidium

11Patient Discharge Instructions/pdi36

copy discharge instructions

›Cryptosporidiosis home care instructions

›Fluids and diet

›Drink oral rehydration solution or clear fluids in small sips frequently

›Avoid dairy products until diarrhea resolves

›BRAT diet or small frequent meals may improve tolerance

›Avoid alcohol

›Medications

›Take nitazoxanide with food if prescribed

›Complete the full course as directed

›Loperamide as directed for symptom relief only if prescribed

›Infection prevention

›Wash hands thoroughly with soap and water after using the toilet

›Alcohol-based hand sanitisers are NOT effective against Cryptosporidium oocysts

›Soap and water required for oocyst removal

›Avoid swimming in pools or recreational water for at least 2 weeks after diarrhea resolves

›Oocysts are chlorine-resistant and can contaminate pools

›Avoid preparing food for others while symptomatic

›Household contacts should practice strict hand hygiene

›Return to emergency department immediately for

›Inability to keep any fluids down

›Persistent vomiting

›Bloody diarrhea

›Severe abdominal pain or right upper quadrant pain

›Fever persisting or worsening

›Dizziness, fainting, or confusion

›Very dark urine or not urinating

›Rapid worsening of symptoms

12References/r22

Guidelines and key sources

›Primary clinical guidelines

›IDSA/HIVMA guidelines for prevention and treatment of opportunistic infections in adults and adolescents with HIV 2025

›Benson C, Brooks J, Dhanireddy S, et al.

›Infectious Diseases Society of America and Office of AIDS Research Advisory Council

›DHHS paediatric OI guidelines 2025

›Kapogiannis BG, Yates F, Li W, et al.

›Guidelines for prevention and treatment of opportunistic infections in children with and exposed to HIV

›IDSA clinical practice guidelines for diagnosis and management of infectious diarrhea 2017

›Shane AL, Mody RK, Crump JA, et al.

›Clinical Infectious Diseases

›Key clinical references

›Pyzocha N, Cuda A. Common Intestinal Parasites. American Family Physician. 2023

›Clinical management reference for cryptosporidiosis in primary care and emergency settings

›Chen XM, Keithly JS, Paya CV, LaRusso NF. Cryptosporidiosis. New England Journal of Medicine. 2002

›Foundational review of pathophysiology and treatment

›Checkley W, White AC, Jaganath D, et al. Review of the global burden, novel diagnostics, therapeutics, and vaccine targets for Cryptosporidium. Lancet Infectious Diseases. 2015

›Cohn IS, Henrickson SE, Striepen B, Hunter CA. Immunity to Cryptosporidium: Lessons from acquired and primary immunodeficiencies. Journal of Immunology. 2022

›Semenza JC, Ko AI. Waterborne diseases that are sensitive to climate variability and climate change. New England Journal of Medicine. 2023

›Coding references

›ICD-10 A07.2 cryptosporidiosis

›SNOMED CT cryptosporidiosis disorder concept

›FDA drug label nitazoxanide Alinia for cryptosporidiosis dosing

Evidence & Review

Evidence & Review