Out of 83 patients with severe anaphylaxis, 1 had a probable biphasic allergic reaction, which was mild and consisted of rash only. No patients developed true biphasic anaphylaxis.
Adults with cough <3weeks or 3-8 weeks with post-tussive vomiting or whooping should be treated for pertussis; those with fever or without paroxysmal cough should be considered to have an alternate diagnosis. Children with <4 weeks of cough and post-tussive vomiting may have pertussis, but it was much less clear than in adults.
No clinical criteria were powerful diagnostic discriminators of the presence or absence of pneumonia in children, though some were fair. When in doubt, a CXR is probably warranted, with the exceptions of obvious bronchiolitis or asthma. Low SpO2 (</= 95 to 96%) or increased work of breathing were the best predictors of radiographic pneumonia in children; auscultatory findings and tachypnea were poor. You don't need a CXR if no cough, no fever, no tachypnea, and normal SpO2.
I couldn't state it better than the author's conclusion: "In adult patients, the presence of whooping or posttussive vomiting should rule in a possible diagnosis of pertussis, whereas the lack of a paroxysmal cough or the presence of fever should rule it out. In children, posttussive vomiting is much less helpful as a clinical diagnostic test."