Stage 3 — Prioritize hypotheses. At 0800 on hospital day 4, the 74-year-old client receiving ceftriaxone and azithromycin for community-acquired pneumonia (ciprofloxacin two months ago) has passed six watery stools since 0400 with mild cramping and no visible blood. She has had no laxative or stool softener in 48 hours, is lightheaded on standing, and now feels unsafe walking. Temperature is 37.9 C after 48 hours afebrile, heart rate 96/min (74 yesterday), BP 118/72 mm Hg, SpO2 96% on room air, and crackles are fewer than on admission. WBC is 14.2 x 10^9/L (9.1 yesterday), procalcitonin has fallen from 1.8 to 0.3 ng/mL, lactate is 1.4 mmol/L, and creatinine is 1.1 mg/dL (baseline 1.0). The abdomen is soft. Stool testing has not yet been sent. Complete the diagram by selecting the condition the client is most likely experiencing, 2 actions the nurse should take to address that condition, and 2 parameters the nurse should monitor to assess the client's progress.

Quick answer
Condition: suspected C. difficile infection. Actions: start contact precautions in a private room now and send one loose stool for C. difficile testing. Monitor: stool number and consistency per day and orthostatic blood pressure and heart rate.

Why this is correct
New watery diarrhea (3 or more unformed stools in 24 hours) after antibiotic exposure, with no laxative to explain it, is the testing trigger for C. difficile. The new fever and the WBC jump from 9.1 to 14.2 add weight. Precautions are started on suspicion, not after the result, because spores spread on hands and surfaces before a test returns. Only unformed stool is tested. The client is losing fluid (lightheaded, heart rate up from 74 to 96), so stool output and orthostatic vital signs are the numbers that show whether she is getting better or drying out.

Easy analogy or mental picture
Think of C. difficile spores as glitter: once it is out, it is on every surface, and a quick alcohol wipe just moves it around. You close the room (precautions) and physically wash it off with soap and water.

Memory hook
Antibiotics + new watery stools + no laxative = test one loose stool and gown up now.

NCLEX decision rule
When an infection is suspected and spreads by contact, start the precautions at the moment of suspicion; do not wait for confirmation. Choose monitoring parameters that measure the problem itself (stool output) and its main complication (volume loss).

Why the other choices are wrong
Fulminant infection needs hypotension, ileus, rising lactate, or distention; this client has a normal BP, lactate 1.4, and a soft abdomen. Worsening pneumonia is tempting because of the fever and WBC, but procalcitonin is falling and crackles are fewer, so blood and sputum cultures and procalcitonin or SpO2 tracking follow the wrong problem. An osmotic bowel-regimen cause is excluded because no laxative was given in 48 hours. Loperamide is avoided because slowing the bowel in suspected C. difficile can hide worsening and raise the risk of colonic dilation. Alcohol rub does not kill spores; soap-and-water handwashing is needed. Occult blood does not track C. difficile activity or hydration.