Contamination with HIV antibody may be responsible for false positive results in specimens tested on automated platforms running HIV 4th generation assays in a region of high HIV prevalence

<div><p>Introduction</p><p>In South Africa where the prevalence of HIV infection is very high, 4^th generation HIV antibody/p24 antigen combo immunoassays are the tests of choice for laboratory based screening. Testing is usually performed in clinical pathology laboratories on automated analysers. To investigate the cause of false positive results on 4^th generation HIV testing platforms in public sector laboratories, the performance of two automated platforms was compared in a clinical pathology setting, firstly on routine diagnostic specimens and secondly on known sero-negative samples.</p><p>Methods</p><p>Firstly, 1181 routine diagnostic specimens were sequentially tested on Siemens and Roche automated 4^th generation platforms. HIV viral load, western blot and follow up testing were used to determine the true status of inconclusive specimens. Subsequently, known HIV seronegative samples from a single donor were repeatedly tested on both platforms and an analyser was tested for surface contamination with HIV positive serum to identify how suspected specimen contamination could be occurring.</p><p>Results</p><p>Serial testing of diagnostic specimens yielded 163 weakly positive or discordant results. Only 3 of 163 were conclusively shown to indicate true HIV infection. Specimen contamination with HIV antibody was suspected, based on the following evidence: the proportion of positive specimens increased on repeated passage through the analysers; viral loads were low or undetectable and western blots negative or indeterminate on problem specimens; screen negative, 2^nd test positive specimens tested positive when reanalysed on the screening assay; follow up specimens (where available) were negative. Similarly, an increasing number of known negative specimens became (repeatedly) sero-positive on serial passage through one of the analysers. Internal and external analyser surfaces were contaminated with HIV serum, evidence that sample splashes occur during testing.</p><p>Conclusions</p><p>Due to the extreme sensitivity of these assays, contamination with minute amounts of HIV antibody can cause a negative sample to test positive. Better contamination control measures are needed on analysers used in clinical pathology environments, especially in regions where HIV sero-prevalence is high.</p></div

Tanapox, South Africa, 2022

Tanapox is a rarely diagnosed zoonosis known to be endemic to equatorial Africa. All previously reported human cases were acquired within 10° north or south of the Equator, most recently 19 years ago. We describe a human case of tanapox in South Africa (24° south of the Equator). Expanded surveillance for this pathogen is warranted

Cytomegalovirus viral load kinetics in patients with HIV/AIDS admitted to a medical intensive care unit: a case for pre-emptive therapy.

BACKGROUND: Cytomegalovirus (CMV) infection is associated with severe diseases in immunosuppressed patients; however, there is a lack of data for pre-emptive therapy in patients with HIV/AIDS. METHOD: This was a retrospective study, which enrolled patients diagnosed with HIV/AIDS (CD41,000 copies/ml at baseline testing had significantly higher mortality compared to those who had 5,100 copies/ml and did not receive ganciclovir had 100% mortality compared to 58% mortality in those who received ganciclovir at VLs of >5,100 copies/ml, 50% mortality in those who were not treated and had low VLs of <5,100 copies/ml, and 44% mortality in those who had ganciclovir treatment at VLs of <5,100 copies/ml (p = 0.084, 0.046, 0.037, respectively). CONCLUSION: This study showed a significantly increased mortality in patients with HIV/AIDS who had high CMV VLs, and suggests that a threshold value of 1,000 copies/ml may be appropriate for pre-emptive treatment in this group

Determining sero-positivity at first and second testing episodes.

<p>The number of negative results decreased and the number of positive results increased on second testing on the Roche analyser at UN laboratory.</p

Western blots of selected specimens: negative, positive and low positive controls are labelled N, P and LP respectively.

<p>Specimens of interest are labelled A to G. Specimens A, B and C were concordantly weakly positive on both serology assays and HIV viral loads were high. Their western blots were scored as positive (A) and indeterminate (B, C). Specimens D, E, F and G were also WB indeterminate, but RNA negative. A follow up specimen on D was antibody negative.</p

Study plan.

<p>(a) 1181 consecutive routine diagnostic samples (serum or plasma) tested on the Siemens HIV 4^th generation platform at the primary testing laboratories were re-tested on the Roche platform at the referral laboratory UN (using the same primary tube). Inconclusive specimens were further investigated with HIV viral load and western blot where specimen volume permitted. A subset of 26 specimens which were screen negative, second test positive was retested on the Siemens (initial screening assay) at the JE laboratory. (b) 210 known HIV antibody negative, NAT negative specimens from the same donor were tested on the Siemens and Roche platforms at JE and UN respectively. 105 specimens were tested on each analyser over a 10 day period and handled as normal clinical specimens. After the initial HIV serology test, the specimens were sent through the same analyser and tested for a second time.</p

S/CO values of false positive samples from Siemens analyser at JE laboratory.

<p>S/CO values of false positive samples from Siemens analyser at JE laboratory.</p

Clinical characteristics of patients who had undetectable CMV VL at baseline.

<p>ID = identity, CMV VL = cytomegalovirus viral load, ICU = intensive care unit, ET = early treatment,</p><p>DT = delayed treatment, nt-LVL = non-treatment and low viral load, ND = not done, N/A – ganciclovir was not administered as some of these patients were admitted at a time when a 10000 copies/ml threshold for CMV treatment was used, LDL = lower than detectable limit. For consistency, sample collection dates were used for CMV VL results.</p

Characteristics of patients in different groups stratified by CMV VL of 5100 copies/ml and ganciclovir use.

<p>ET = early treatment, DT = delayed treatment, nt-LVL = non-treatment and low viral load, nt-HVL = non-treatment and high viral load, TB = tuberculosis, ICU = intensive care unit.</p>†<p> = highest CMV VL values per patient were used for this analysis.</p

Figure 2

<p>Kaplan-Meier curve analysis showing survival probalities between the groups of patients: (A) who had CMV viral loads <1000 copies/ml compared to those who had viral loads >1000 copies/ml at baseline testing, (B) who had CMV viral loads <5000 copies/ml compared to those who had viral loads >5000 copies/ml at baseline testing, (C) who had CMV viral loads <10000 copies/ml compared to those who had viral loads >10000 copies/ml at baseline testing. HR = hazard ratio, CI = confidence interval.</p