Estimating the impact of cefuroxime versus cefazolin and amoxicillin/clavulanate use on future collateral resistance: a retrospective comparison.

BACKGROUND: Quantitative estimates of collateral resistance induced by antibiotic use are scarce. OBJECTIVES: To estimate the effects of treatment with amoxicillin/clavulanate or cefazolin, compared with cefuroxime, on future resistance to ceftazidime among hospitalized patients. METHODS: A retrospective analysis of patients with positive bacterial cultures hospitalized in an Israeli hospital during 2016-19 was conducted. Patients were restricted to those treated with amoxicillin/clavulanate, cefazolin or cefuroxime and re-hospitalized with a positive bacterial culture during the following year. Matching was performed using exact, Mahalanobis and propensity score matching. Each patient in the amoxicillin/clavulanate and cefazolin groups was matched to a single patient from the cefuroxime group, yielding 185:185 and 298:298 matched patients. Logistic regression and the g-formula (standardization) were used to estimate the OR, risk difference (RD) and number needed to harm (NNH). RESULTS: Cefuroxime induced significantly higher resistance to ceftazidime than amoxicillin/clavulanate or cefazolin; the marginal OR was 1.76 (95% CI = 1.16-2.83) compared with amoxicillin/clavulanate and 1.98 (95% CI = 1.41-2.8) compared with cefazolin and the RD was 0.118 (95% CI = 0.031-0.215) compared with amoxicillin/clavulanate and 0.131 (95% CI = 0.058-0.197) compared with cefazolin. We also estimated the NNH; replacing amoxicillin/clavulanate or cefazolin with cefuroxime would yield ceftazidime resistance in 1 more patient for every 8.5 (95% CI = 4.66-32.14) or 7.6 (95% CI = 5.1-17.3) patients re-hospitalized in the following year, respectively. CONCLUSIONS: Our results indicate that treatment with amoxicillin/clavulanate or cefazolin is preferable to cefuroxime, in terms of future collateral resistance. The results presented here are a first step towards quantitative estimations of the ecological damage caused by different antibiotics.

The Effect of Macrolides on Mortality in Bacteremic Pneumococcal Pneumonia: A Retrospective, Nationwide Cohort Study, Israel, 2009-2017.

BACKGROUND: Previous cohort studies of pneumonia patients reported lower mortality with advanced macrolides. Our aim was to characterize antibiotic treatment patterns and assess the role of quinolones or macrolides in empirical therapy. MATERIALS: An historical cohort, 1 July 2009 to 30 June 2017, included, through active surveillance, all culture-confirmed bacteremic pneumococcal pneumonia (BPP) among adults in Israel. Cases without information on antibiotic treatment were excluded. Logistic regression analysis was used to assess independent predictors of in-hospital mortality. RESULTS: A total of 2016 patients with BPP were identified. The median age was 67.2 years (interquartile range [IQR] 53.2-80.6); 55.1% were men. Lobar pneumonia was present in 1440 (71.4%), multi-lobar in 576 (28.6%). Median length of stay was 6 days (IQR 4-11). A total of 1921 cases (95.3%) received empiric antibiotics with anti-pneumococcal coverage: ceftriaxone, in 1267 (62.8%). Coverage for atypical bacteria was given to 1159 (57.5%), 64% of these, with macrolides. A total of 372 (18.5%) required mechanical ventilation, and 397 (19.7%) died. Independent predictors of mortality were age (odds ratio [OR] 1.051, 95% confidence interval [CI] 1.039, 1.063), being at high-risk for pneumococcal disease (OR 2.040, 95% CI 1.351, 3.083), multi-lobar pneumonia (OR 2.356, 95% CI 1.741, 3.189). Female sex and macrolide therapy were predictors of survival: (OR 0.702, 95% CI .516, .955; and OR 0.554, 95% CI .394, .779, respectively). Either azithromycin or roxithromycin treatment for as short as two days was predictor of survival. Quinolone therapy had no effect. CONCLUSIONS: Empirical therapy with macrolides reduced odds for mortality by 45%. This effect was evident with azithromycin and with roxithromycin. The effect did not require a full course of therapy.

Community antibiotic prescriptions during COVID-19 era: a population-based cohort study among adults.

OBJECTIVES: This study investigated the association between the COVID-19 pandemic and antibiotic prescription ratios and the determinants of antibiotic prescription in the community. METHODS: The study was based on a retrospective population cohort of adults in a community setting. Antibiotic prescription ratios from March 1, 2020 to February 28, 2021 (COVID-19 period) were compared to similar months in previous years. Differences in visit type, infectious disease-related visit, and antibiotic prescription ratios during these visits were compared. A logistic regression model was used to identify independent determinants of antibiotic prescription during the study period. RESULTS: The cohort included almost 3 million individuals with more than 33 million community medical encounters per year. In the COVID-19 period, the antibiotic prescription ratio decreased 45% (from 34.2 prescriptions/100 patients to 19.1/100) compared to the previous year. Visits due to an infectious disease etiology decreased by 10% and prescriptions per visit decreased by 39% (from 1 034 425 prescriptions/3 764 235 infectious disease visits to 587 379/3 426 451 respectively). This decrease was observed in both sexes and all age groups. Telemedicine visits were characterized by a 10% lower prescription ratio compared to in-person visits. Thus, a threefold increase in telemedicine visits resulted in a further decrease in prescription ratios. The COVID-19 period was independently associated with a decrease in antibiotic prescription, with an OR of 0.852 (95% CI 0.848-0.857). DISCUSSION: We describe a significant decrease in antibiotic prescription ratios during the COVID-19 periods that was likely related to a decrease in the incidence of certain infectious diseases, the transfer to telemedicine, and a change in prescription practices among community-based physicians.

How compassionate use enabled Israel to deliver the Pfizer-BioNTech COVID-19 vaccination to vulnerable children aged 12-15 years before regulatory approval.

AIM: This paper describes the emergency, compassionate use of the COVID-19 vaccination for high-risk adolescents aged 12-15 years prior to approval by the American Food and Drugs Administration in May 2021. The target audience had underlying health conditions associated with severe disease and multisystem inflammatory syndrome in children (MIS-C) or severely immunosuppressed household members. METHODS: An orderly approval system was established in Israel for adolescents aged 12-15 years, based on a professional position paper and compassionate treatment regulations. From 12 February 2021, eligible adolescents were referred to the Israeli Ministry of Health for permission to vaccinate, via four health maintenance organisations. Data were collected about adverse events after vaccinations and the incidence of any cases of COVID-19. RESULTS: By 15 March 2021, the vaccine had been approved for 607 adolescents: 333 had received one dose, and 92 had received two doses. The median age was 14.6 years, and the major indication was obesity. Only one child tested positive for the virus, 4 days after vaccination, and no adverse effects were recorded. CONCLUSION: The emergency use of COVID-19 vaccination for 333 adolescents aged 12-15, 92 of them with 2 doses, based on a position paper and compassionate treatment regulations, did not result in any adverse effects. Since 27 July 2021, the same process was further applied in Israel among younger children, aged 5-11, preceding formal release of the clinical trial.

Validation of a semiautomated system for surveillance of surgical site infection after cesarean section.

Surveillance of surgical site infection after cesarean section is challenging due to the high volume of these surgeries. A manual chart review of women undergoing cesarean section between January and June 2017 (675 charts, 40 infections) was compared to charts identified via an algorithm (141 charts, 39 infections). The algorithm achieved 97.5% sensitivity and 83.9% specificity and reduced the workload of infection control personnel.

Nosocomial outbreak caused by the SARS-CoV-2 Delta variant in a highly vaccinated population, Israel, July 2021.

A nosocomial outbreak of SARS-CoV-2 Delta variant infected 42 patients, staff and family members; 39 were fully vaccinated. The attack rate was 10.6% (16/151) among exposed staff and reached 23.7% (23/97) among exposed patients in a highly vaccinated population, 16-26 weeks after vaccination (median: 25 weeks). All cases were linked and traced to one patient. Several transmissions occurred between individuals wearing face masks. Fourteen of 23 patients became severely sick or died, raising a question about possible waning immunity.

Healthcare-associated Pneumocystis jirovecii Pneumonia (PJP) Infection in HIV-negative Adults: a Multicenter Study.

BACKGROUND: Pneumocystis jirovecii pneumonia (PJP) is an opportunistic infection in immunocompromised patients. Clusters of PJP, especially among organ transplant recipients in clinic settings were described. Data regarding nosocomial PJP infection among inpatients are limited. OBJECTIVES: To assess the magnitude and characteristics of inpatient healthcare-associated PJP infection (HCA-PJP) in HIV-negative patients. METHODS: A retrospective chart review of hospitalized PJP patients was performed to identify HCA-PJP. The study was performed at six medical centers in Israel from 2006 to 2016. HCA-PJP was defined as cases of hospital-onset or those with documented contact with a PJP patient. We reviewed and cross-matched temporal and spatial co-locations of patients. Clinical laboratory characteristics and outcomes were compared. RESULTS: Seventy-six cases of PJP were identified. Median age was 63.7 years; 64% men; 44% hematological malignancies; 18% inflammatory diseases; and 61% steroid usage. Thirty-two patients (42%) were defined as HCA-PJP: 18/32 (23.6%) were hospitalized at onset and 14/32 (18.4%) had a previous encounter with a PJP patient. Time from onset of symptoms to diagnosis was shorter in HCA-PJP vs. community-PJP (3.25 vs. 11.23 days, P = 0.009). In multivariate analysis, dyspnea at presentation (odds ratio [OR] 16.79, 95% confidence interval [95%CI] 1.78-157.95) and a tendency toward higher rate of ventilator support (72% vs. 52%, P = 0.07, OR 5.18, 95%CI 0.7-30.3) were independently associated with HCA-PJP, implying abrupt disease progression in HCA-PJP. CONCLUSIONS: HCA-PJP was common. A high level of suspicion for PJP among selected patients with nosocomial respiratory infection is warranted. Isolation of PJP patients should be considered.

Rituximab identified as an independent risk factor for severe PJP: A case-control study.

OBJECTIVE: Pneumocystis jirovecii pneumonia (PJP) was reported among immunosuppressed patients with deficits in cell-mediated immunity and in patients treated with immunomodulatory drugs. The aim of this study was to identify risk-factors for PJP in noninfected HIV patients. METHODS: This retrospective, test negative, case-control study was conducted in six hospitals in Israel, 2006-2016. Cases were hospitalized HIV-negative patients with pneumonia diagnosed as PJP by bronchoalveolar lavage. Controls were similar patients negative for PJP. RESULTS: Seventy-six cases and 159 controls were identified. Median age was 63.7 years, 65% males, 34% had hematological malignancies, 11% inflammatory diseases, 47% used steroids and 9% received antilymphocyte monoclonal antibodies. PJP was independently associated with antilymphocyte monoclonal antibodies (OR 11.47, CI 1.50-87.74), high-dose steroid treatment (OR 4.39, CI 1.52-12.63), lymphopenia (OR 8.13, CI 2.48-26.60), low albumin (OR 0.15, CI 0.40-0.54) and low BMI (OR 0.80, CI 0.68-0.93). CONCLUSION: In conclusion, rituximab, which is prescribed for a wide variety of malignant and inflammatory disorders, was found to be significant risk-factor for PJP. Increased awareness of possible PJP infection in this patient population is warranted.

Characterization of Congenital Toxoplasmosis in Israel: A 17-year Nationwide Study Experience.

BACKGROUND: Congenital toxoplasmosis (CT) can cause significant neurologic manifestations and other untoward sequelae. Neither the current epidemiology nor the disease severity of CT in Israel is known. METHODS: Records of CT were collected from the National Toxoplasmosis Reference Laboratory and from 15 medical centers across Israel between 2001 and 2017. Eligible case-patients were fetuses or infants <12 months of age at the time of diagnosis. RESULTS: Of the 43 CT cases identified, 24 (55%) were in Jews and the remaining 19 cases were in patients of Arab (non-Bedouin) origin. The overall annual estimated rate of symptomatic CT was calculated as 0.55 per 100,000 live births. One or more severe clinical manifestations were reported in 12 (46%) of the 28 live-born infants and included cerebral calcifications (7 cases), chorioretinitis (4 cases), hydrocephalus (2 cases) and 1 case of death. Sensitivities of blood polymerase chain reaction (PCR), cerebrospinal fluid PCR and IgM antibody tests were 50% each. However, analyzing PCR samples from both sites, together with IgM testing, increased the sensitivity to 93%. CONCLUSIONS: The relative rate of severe manifestations was higher than in previous European reports. It is possible that the greater disease severity observed in Israel is in part due to the lack of systematic antenatal treatment and screening. Arab (non-Bedouin) infants are at higher risk for contracting CT. Performing serologic and PCR tests simultaneously is essential to improve CT diagnosis. This study demonstrates a need for an educational program to target high-risk populations.

Quinolone Consumption by Mothers Increases Their Children's Risk of Acquiring Quinolone-Resistant Bacteriuria.

BACKGROUND: Quinolone resistance has been documented in the pediatric population, although their use is limited in children. This study investigated the effect of maternal quinolone use on gram-negative bacterial resistance to quinolones in their offspring. METHODS: We conducted a population-based, unmatched case-control study during 2010-2017. Cases were all children aged 0.5-17 years with community acquired, gram-negative quinolone-resistant bacteriuria. Controls were similar children with quinolone-sensitive bacteriuria. Only the first positive urine cultures for each child were included. Data on quinolones dispensed to the mother, any antibiotics dispensed to the children, age, sex, ethnicity, and prior hospitalizations were collected. Children with previous quinolone use were excluded. RESULTS: The study population consisted of 40 204 children. Quinolone resistance was detected in 2182 (5.3%) urine cultures. The median age was 5 years, with 93.7% females and 77.6% Jewish. A total of 26 937 (65%) of the children received any antibiotic and 1359 (3.2%) of the mothers received quinolones in the 6 months preceding bacteriuria. Independent risk factors were quinolone dispensed to the mothers (odds ratio [OR], 1.50 [95% confidence interval {CI}, 1.22-1.85]), Arab ethnicity (OR, 1.99 [95% CI, 1.81-2.19]), and antibiotic dispensed to the child (OR, 1.54 [95% CI, 1.38-1.71]). Compared with children aged 12-17 years, younger children had 1.33-1.43 increased odds for quinolone-resistant bacteriuria. CONCLUSIONS: Quinolone prescription to mothers was linked to increased risk of community-acquired, quinolone-resistant bacteria in their offspring, by about 50%. This is another example of the deleterious ecological effects of antibiotic use and should be considered when prescribing antibiotics.

Antibiotic Exposure in the Community and Resistance Patterns of Escherichia coli Community-Acquired Bloodstream Infection.

BACKGROUND: Increasing antibiotic resistance in the community results in greater use of empiric broad spectrum antibiotics for patients at hospital admission. As a measure of antibiotic stewardship it is important to identify a patient population that can receive narrow spectrum antibiotics. OBJECTIVES: To evaluate resistance patterns of Escherichia coli bloodstream infection (BSI) from strictly community-acquired infection and the impact of recent antibiotic use on this resistance. METHODS: This single center, historical cohort study of adult patients with E. coli BSI was conducted from January 2007 to December 2011. Patients had no exposure to any healthcare facility and no chronic catheters or chronic ulcers. Data on antibiotic use during the previous 90 days was collected and relation to resistance patterns was assessed. RESULTS: Of the total number of patients, 267 BSI cases met the entry criteria; 153 patients (57%) had bacteria sensitive to all antibiotics. Among 189 patients with no antibiotic exposure, 61% of isolates (116) were pan-sensitive. Resistance to any antibiotic appeared in 114 patients and 12 were extended-spectrum beta-lactamase (ESBL) producers. Quinolone use was the main driver of resistance to any antibiotic and to ESBL resistance patterns. In a multivariate analysis, older age (odds ratio 1.1) and quinolone use (odds ratio 7) were independently correlated to ESBL. CONCLUSIONS: At admission, stratification by patient characteristics and recent antibiotic use can help personalize primary empirical therapy.

A Population-Structured HIV Epidemic in Israel: Roles of Risk and Ethnicity.

BACKGROUND: HIV in Israel started with a subtype-B epidemic among men who have sex with men, followed in the 1980s and 1990s by introductions of subtype C from Ethiopia (predominantly acquired by heterosexual transmission) and subtype A from the former Soviet Union (FSU, most often acquired by intravenous drug use). The epidemic matured over the last 15 years without additional large influx of exogenous infections. Between 2005 and 2013 the number of infected men who have sex with men (MSM) increased 2.9-fold, compared to 1.6-fold and 1.3-fold for intravenous drug users (IVDU) and Ethiopian-origin residents. Understanding contemporary spread is essential for effective public health planning. METHODS: We analyzed demographic and virologic data from 1,427 HIV-infected individuals diagnosed with HIV-I during 1998-2012. HIV phylogenies were reconstructed with maximum-likelihood and Bayesian methods. RESULTS: Subtype-B viruses, but not A or C, demonstrated a striking number of large clusters with common ancestors having posterior probability ≥0.95, including some suggesting presence of transmission networks. Transmitted drug resistance was highest in subtype B (13%). MSM represented a frequent risk factor in cross-ethnic transmission, demonstrated by the presence of Israeli-born with non-B virus infections and FSU immigrants with non-A subtypes. CONCLUSIONS: Reconstructed phylogenetic trees demonstrated substantial grouping in subtype B, but not in non-MSM subtype-A or in subtype-C, reflecting differences in transmission dynamics linked to HIV transmission categories. Cross-ethnic spread occurred through multiple independent introductions, with MSM playing a prevalent role in the transmission of the virus. Such data provide a baseline to track epidemic trends and will be useful in informing and quantifying efforts to reduce HIV transmission.

Impact of quinolone restriction on resistance patterns of Escherichia coli isolated from urine by culture in a community setting.

BACKGROUND: Decreased antimicrobial susceptibility after increased antibiotic use is a known phenomenon. Restoration of susceptibility once antimicrobial use is decreased is not self-evident. Our objective was to evaluate, in a community setting, the impact of quinolone restriction on the antimicrobial resistance of E. coli urine isolates. METHODS: We conducted a retrospective, quasi-experimental ecological study to assess the proportion of quinolone-susceptible E. coli urine isolates in the periods before, during, and after a nationwide restriction on ciprofloxacin use was implemented. We used an interrupted time interval analysis for outcome evaluation. RESULTS: We found a significant decline in quinolone consumption, measured as defined daily doses (DDDs) per month, between the preintervention and intervention periods (point estimate, -1827.3 DDDs per month; 95% confidence interval [CI], -2248.8 to -1405.9 DDDs per month; p < .001). This decline resulted in a significant decrease in E. coli nonsusceptibility to quinolones, from a mean of 12% in the preintervention period to a mean of 9% in the intervention period (odds ratio, 1.35; p = .014). The improved susceptibility pattern reversed immediately when quinolone consumption rose. Moreover, a highly significant inverse relationship was found between the level of quinolone use (regardless of intervention period) and the susceptibility of E. coli urine isolates to quinolone (odds ratio, 1.70; 95% CI, 1.26-2.28). During the months of highest quinolone use (8321 DDDs per month), the proportion of nonsusceptibility was 14%, whereas during the months of lowest quinolone use (4027 DDDs per month), the proportion of nonsusceptibility was 9%. An average decrease in resistance of 1.16% was observed for each decrease of 1000 DDDs. CONCLUSION: Reducing quinolone consumption can lead to an immediate increase in the susceptibility of E. coli urine isolates to quinolones.

Hospital-wide methicillin-resistant Staphylococcus aureus control program: A 5-year follow-up.

We investigated the influence of different interventions (active surveillance, contact isolation, monitoring, and rapid diagnostic testing) on the number of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia cases. An interrupted time-series analysis was used. MRSA bacteremia cases were reduced by 70% when all interventions were in place. We proved monitoring to be an essential component.

Reporting of adverse events in randomized controlled trials of highly active antiretroviral therapy: systematic review.

OBJECTIVES: Our objectives were to systematically assess the quality of reporting of adverse events (AEs) in publications of randomized trials of highly active antiretroviral therapy (HAART), and to examine whether reporting quality affects the effect estimates reported for AEs. METHODS: We searched the PubMed, Cochrane library and EMBASE electronic databases up to December 2008. We included all published randomized controlled trials assessing HAART for treatment-naive adult HIV-infected individuals, with 48 weeks' follow-up. The quality of AE reporting was extracted according to CONSORT guidelines. We pooled the relative risks for AEs and compared results by sponsorship and different reporting methods. RESULTS: Forty-nine trials, including 19 882 patients, published between 2000 and 2008, met the inclusion criteria. Only one of the trials reported on AE collection methods. Twenty-six trials reported only AEs attributed to drugs, 17 of which did not refer to the attribution methods. AE reporting was nearly always selective and selection criteria were highly variable, based on severity grading or occurrence threshold. Presentation of AEs above an occurrence threshold was more common in studies sponsored by industry (30/31) than in studies sponsored by non-profit organizations (3/18). Moreover, we showed that differences in the methods of reporting AEs may affect the results reported for AEs. No significant improvement in AE reporting was seen over this period. CONCLUSIONS: We found substantial variability in AE reporting. Variability was influenced by sponsor identity and affected outcomes. These facts obstruct our ability to choose HAART based on currently published data.

Active surveillance for methicillin-resistant Staphylococcus aureus (MRSA) decreases the incidence of MRSA bacteremia.

OBJECTIVES: To evaluate the influence of performance of active surveillance cultures for methicillin-resistant Staphylococcus aureus (MRSA) on the incidence of nosocomial MRSA bacteremia in an endemic hospital. DESIGN: Before-after trial. SETTING: A 700-bed hospital. PATIENTS: All patients admitted to the hospital who were at high risk for MRSA bacteremia. INTERVENTION: Performance of surveillance cultures for detection of MRSA were recommended for all patients at high risk, and contact isolation was implemented for patients with positive results of culture. Each MRSA-positive patient received one course of eradication treatment. We compared the total number of surveillance cultures, the percentage of surveillance cultures with positive results, and the number of MRSA bacteremia cases before the intervention (from January 2002 through February 2003) after the start of the intervention (from July 2003 through October 2004). RESULTS: The number of surveillance cultures performed increased from a mean of 272.57 cultures/month before the intervention to 865.83 cultures/month after the intervention. The percentage of surveillance cultures with positive results increased from 3.13% before to 5.22% after the intervention (P < .001). The mean number of MRSA bacteremia cases per month decreased from 3.6 cases before the intervention to 1.8 cases after the intervention (P < 0.001). CONCLUSIONS: Active surveillance culture is important for identifying hidden reservoirs of MRSA. Contact isolation can prevent new colonization and infection and lead to a significant reduction of morbidity and healthcare costs.

Comparative performance of the Amplicor HIV-1 Monitor Assay versus NucliSens EasyQ in HIV subtype C-infected patients.

In facing global programs for treating HIV-infected patients in the developing countries, there is a real need for viral load assays that are accurate for the local subtypes. The present study was designed to evaluate viral load measurements using the newer version of the NASBA assay in subtype C-infected patients. The performances of this new version, a real-time nucleic acid sequence-based amplification HIV-1 assay (NucliSens EasyQ), were compared to Amplicor HIV-1 Monitor Assay version 1.5 in 79 samples of subtype C-infected patients originating from Ethiopia. Twenty HIV-1 subtype B-infected patients served as a control group. Blood samples from patients in both groups were tested by both assays. The results were compared by a paired, two-tailed Student's t-test. The disparity between the results of the two viral load assays was highly significant in subtype C samples (P = 0.005), such that in the vast majority, higher values of viral load were obtained by the Amplicor assay. However, no differences between the two assays were found in subtype B samples (P = 0.77). CD4 measurements were available for 78 samples of subtype C-infected patients. Of these, a CD4-to-viral load discrepancy (CD4

Measurement of HIV RNA in patients infected by subtype C by assays optimized for subtype B results in an underestimation of the viral load.

Quantitation assays of HIV-1 RNA used currently were designed and optimized for subtype B viruses. However, infection with non-B HIV viruses has become more common worldwide. Unfortunately, little information is available regarding the suitability of these assays for measurement of viral load in specific non-B subtypes. The performance of two commercial HIV-1 RNA quantitation assays was evaluated in 82 HIV subtype C-infected patients and in 43 HIV-1 subtype B-infected patients. Blood samples were tested by the Amplicor HIV-1 Monitor Assay, Version 1.5, and by the nucleic acid sequence-based amplification HIV-1 assay (NucliSens). The results were compared by using a paired, two-tailed Student's t-test; the difference between the assays was found to be significant only for subtype C. Discordant results (>0.5 log difference) between the two assays were detected in 39% of subtype C samples, compared to 23.2% of subtype B samples. In all cases in which a discordant result was detected, the lower results were obtained by the NucliSens assay. Discordant results between CD4 and viral load (CD4 < 200 cells/ml with a viral load <5,000 copies/ml) were observed in eight of the subtype C-infected patients when a viral load was measured by NucliSens (9.7%), compared to three patients (3.6%) when measured by the Amplicor assay. In conclusion, in patients with HIV subtype C infection, measurement of HIV RNA by the NucliSens assay resulted in a significant underestimation of the viral load as compared to the Amplicor assay. As a consequence, such an underestimation may result in sub-optimal care of patients infected with HIV subtype C.