Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1443 page)

   Following infection with WNV, IgM antibodies are produced and can be detected within 4–7 days after exposure and may persist for about 1 year, while IgG antibodies can be reliably detected from day 8 after infection.

   Limitations

   There are several types of serologic tests routinely used for WNV diagnostics: enzyme-linked immunosorbent assay (ELISA), immunofluorescence assay (IFA), neutralization test (NT), and the hemagglutination inhibition assay.

   Because West Nile IgM may not be positive until up to 8 days following onset of illness, specimens collected <8 days after onset may be negative for IgM, and testing should be repeated.

   A positive West Nile IgG in the absence of a positive West Nile IgM is consistent with past infection with a Flavivirus and does not by itself suggest acute West Nile virus infection.

   If acute West Nile virus infection is suspected, it is best to collect both acute and convalescent sera. Convalescent specimens should be collected 2–3 weeks after acute specimens.

   A major issue in WNV diagnostics is cross-reactivity with antibodies against heterologous flaviviruses, for example, dengue virus (DENV), Japanese encephalitis virus (JEV), tick-borne encephalitis virus (TBEV), or yellow fever virus, which is especially true for IgG antibodies.

WOUND CULTURE

   Definition

   Wound cultures are used to identify pathogenic bacteria causing wound infections. Traumatic injury of tissue may be complicated by infection. Infections may be caused by organisms introduced from the external environment, like bite and surgical and traumatic wounds, or by organisms derived from the patient’s endogenous flora, like peritonitis associated with a ruptured appendix. Wound culture should be considered when a wound shows signs and symptoms typical of infection: swelling, redness, exudate or pus formation, sinus tract formation, pain, swelling, or other.

   Special Collection and Transport Instructions

   Specimens should be collected from the site of active infection. Adjacent areas may show “sympathetic” signs of inflammation, but may not yield relevant pathogens.

   Wash and decontaminate the collection site, typically using a soap and 70% alcohol.