This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
The diagnostic test for rickettsial infection is: 
Select and explain. 
A. Weil-felix reaction, B. WIDAL, C. Sabin test, D. Culture
A: Weil-felix reaction
Answer: A: Weil-felix reaction 
Explanation: Weil-felix reaction