Symptoms of appendicitis (NIDDK.NIH.gov, AAFP):
The first symptom of appendicitis is usually a sudden pain around the belly button that moves to the lower right abdomen within hours. Pain is constant (not crampy) but worsens within hours and is aggravated by coughing and moving around. It often makes a person to lie down on the back (supine) with knees bent to decrease the tension in the abdomen.
Other symptoms that typically develop after pain can include nausea, vomiting (without blood), constipation and diarrhea.
Diagnosis of appendicitis
Blood test shows increased leukocytes (WBC): >10-15,000/μL. If WBC is significantly higher and accompanied with higher temperature than usual for appendicitis (>39 °C) (BMC Surgery - Table 3), the perforation of the appendix or other abdominal organ should be suspected, in which case, the first next imaging investigation would be an abdominal X-ray (AAFP - Fig 6). Abdominal X-ray is not enough for the diagnosis of perforated appendix, so a CT would be needed afterwards. (Ultrasound is usually the first imaging investigation when uncomplicated appendicitis is suspected (Insight Imaging, 2016). The realistic timing between the onset of the first symptoms and worsening of symptoms due to appendix rupture would be 18 hours to 14 days (Annals of African Medicine, 2019), for example, between 24 and 48 hours.
If the worsening of symptoms needs to occur within 2-3 hours, it can be just worsening of appendicitis, because it's unlikely that the appendix would rupture in such a short time. This is also much more realistic than being diagnosed with appendicitis and having a severe GI infection at the same time.
WBC in infections does not need to be as high as you might expect: In one study, WBC in most individuals with pneumococcal pneumonia was 6,000-25,000/mm3 (as compared to 10,000-20,000 in appendicitis).