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rare subtypes
Jul 24, 2001

Dear Dr. Little, I am an ER physician in Chicago. I had a patient that tested negative by EIA, western blot, pcr, and viral culture a year past last possible exposure. But he continues to experience oral signs and symptoms. His oral symptoms resemble that of necrotizing periodontitis. I know that this is usually a sign of severe immunosuppression. But is it possible that he has been infected with a rare subtype not picked up by current tests? His exposure was in Lithuania, and I know that subtype B is not the dominant type there? Could you offer any further advice? Thank you for your help.

Response from Dr. Little

First - very sorry for the delay in answering your question. Regarding testing for rare subtypes - I believe that the available HIV EIA tests all detect non-B subtypes within the M group quite well. On my quick look on the web, I found that subtypes B, C, and D have been identified in Lithuania. The problem is with the non-M group strains - these are group O and N. Group N isolates are vanishingly rare, so I would not worry about these. Group O (for genetic "outliers") are quite uncommon, but less is known about their natural distribution since HIV strains designated group O are not consistently detected by currently licensed EIA tests for HIV-1. Most of the goup O infections have been described in Cameroon or countries bordering Cameroon. Unless your patient has an exposure to someone from this region, I think that group O infection is quite unlikely.

For your patient - I would start with his CD4 cell count and ratio. If it is abnormal (low), then you might want to pursue other immunodeficiency disorders. If you do want to pursue work-up of group O HIV infection, there are subtype-specific serologic techniques (ie. peptide-based enzyme immunoassays) which are available for this purpose. You could contact your state public health department for advice about who/where these tests are done in your state. Good luck.

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