The ectoparasite test detects the presence of rickettsial antibodies in the patient’s serum by performing a nonspecific agglutination reaction with OXl9, OX2, and OXK, which have common bacteriophage antigens with rickettsiae. After the human body is infected by rickettsiae, the serum gradually produces the corresponding antibodies, which appear 5 to 12 days after the onset of the disease and basically disappear after a few months, and the general agglutination value is above 1:160 or the potency rises significantly during the course of the disease has diagnostic significance. The common rickettsial diseases in China are typhus and tsutsugamushi, epidemic typhus mainly for OX19 agglutination price is elevated, tsutsugamushi mainly for OXK elevation is obvious. So, what causes a negative test? The following are the etiologies of a negative test: Rickettsial diseases can be categorized as jungle typhus, urban typhus, epidemic typhus and other rickettsial diseases (which include typhus fever). The various rickettsial diseases are caused by different types of “rickettsiae”. The general symptoms of rickettsial disease resemble a bad cold, with fever, chills, headache, muscle pain, and a rash. Jungle typhus and typhus fever are characterized by penetrating skin ulcers at the site of an infected arthropod bite and painful swelling of nearby lymph glands. Rickettsiosis can cause serious complications and even death. When humans are infected with rickettsiae, epidemic typhus is mainly an increase in the OX19 agglutination value, and the external Fever test is negative. Therefore, timely detection of patients, early isolation, simultaneous extermination of lice, proper treatment; medical observation of close contacts for 14 days.