78 Percent of South Vietnam Bird Flu Patients False Negatives?
Recombinomics Commentary
March 15, 2005
>> Japanese experts are retesting about 100 specimens that a Vietnamese laboratory reported as negative for A(H5N1). "Of the first 30 so-called negative, 11 were found positive, suggesting that that laboratory was missing about one-third of cases," Dr. Stöhr said. <<
The numbers cited above appear to be a later version of earlier reports which indicated that 90 samples from the Pasteur Institute in Ho Chi Minh City were sent to Japan for testing. There were seven false negatives in the first 30 samples tested. These seven were retested in Ho Chi Minh City and four were positive indicating that lab error created 4 false negatives and poor test sensitivity produced 3 more false negatives. The Pasteur Institute was planning on upgrading their monitoring by adopting the test used in Japan.
Repeated e-mails to the New York Times were not answered, so I will use the information reported today as updated information of the earlier results. Prior to yesterday's untested fatality in Kien Giang, there were 10 confirmed H5N1 bird flu cases in southern Vietnam this season. The updated data indicates that 11 of 30 previously reported negative cases were actually H5N1 positive. Extrapolating the 11 of 30 positives to the full 100 would yield 36 more H5N1 positive cases. Thus, of the 110 suspect cases on the south, there were actually 46 positives (10 positives and 36 false negatives). Therefore, the reported cases represented 9% of the suspect cases, while the actual frequency was 42%. Thus, 78% (36/46) of the H5N1 positive cases were missed, not 33% as quoted above.
Unfortunately, data on the three most widely discussed clusters in Thai Binh suggest a similar limitation in testing in the north. Only one of the seven cases was positive on the initial test. One was untested, two were inconclusive, and three were negative. The inconclusive and negative patients were subsequently H5N1 confirmed, although one was negative twice and only positive at autopsy.
It is not clear if the second nurse from Thai Binh is a true negative. Her contact history with one of two H5N1 positive patients and an H5N1 positive nurse, coupled with her bird flu symptoms, raise serious questions about the accuracy of the reported negative result.
In addition to the false negatives described above, until yesterday there were no reported H5N1 cases in the south since the beginning of February. The suspect fatality reported yesterday still had not been confirmed, 10 days after admission.
The inability to accurately test patients admitted to the largest infectious disease hospitals in Vietnam raises serious questions about the WHO plans to rapidly identify, treat, and isolate H5N1 patients and contacts to control pandemic flu spread.
The monitoring of bird flu remains scandalously poor.
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