Evaluation of Vector-Enabled Xenosurveillance in Rural Guatemala

Surveillance methods that permit rapid detection of circulating pathogens in low-resource settings are desperately needed. In this study, we evaluated a mosquito bloodmeal-based surveillance method ("xenosurveillance") in rural Guatemala. Twenty households from two villages (Los Encuentros and Chiquirines) in rural southwest Guatemala were enrolled and underwent weekly prospective surveillance from August 2019 to December 2019 (16 weeks). When febrile illness was reported in a household, recently blood-fed mosquitoes were collected from within dwellings and blood samples taken from each member of the household. Mosquitoes were identified to species and blood sources identified by sequencing. Shotgun metagenomic sequencing was used to identify circulating viruses. Culex pipiens (60.9%) and Aedes aegypti (18.6%) were the most abundant mosquitoes collected. Bloodmeal sources were most commonly human (32.6%) and chicken (31.6%), with various other mammal and avian hosts detected. Several mosquito-specific viruses were detected, including Culex orthophasma virus. Human pathogens were not detected. Therefore, xenosurveillance may require more intensive sampling to detect human pathogens in Guatemala and ecologically similar localities in Central America.

Colorado tick fever virus: a review of historical literature and research emphasis for a modern era

Colorado tick fever virus is an understudied tick-borne virus of medical importance that is primarily transmitted in the western United States and southwestern Canada. The virus is the type species of the genus Coltivirus (Spinareoviridae) and consists of 12 segments that remain largely uncharacterized. Patterns of viral distribution are driven by the presence of the primary vector, the Rocky Mountain wood tick, Dermacentor andersoni. Infection prevalence in D. andersoni can range from 3% to 58% across the geographic distribution of the tick. Infection in humans can be severe and often presents with fever relapses but is rarely fatal. Here, we review the literature from primary characterizations in the early 20th century to current virus/vector research being conducted and identify vacancies in current research.

Safety study of Rift Valley Fever human vaccine candidate (DDVax) in mosquitoes

Rift Valley fever virus (RVFV) is a mosquito-borne pathogen with significant human and veterinary health consequences that periodically emerges in epizootics. RVFV causes fetal loss and death in ruminants and in humans can lead to liver and renal disease, delayed-onset encephalitis, retinitis, and in some cases severe haemorrhagic fever. A live attenuated vaccine candidate (DDVax), was developed by the deletion of the virulence factors NSs and NSm from a clinical isolate, ZH501, and has proven safe and immunogenic in rodents, pregnant sheep and non-human primates. Deletion of NSm also severely restricted mosquito midgut infection and inhibited vector-borne transmission. To demonstrate environmental safety, this study investigated the replication, dissemination and transmission efficiency of DDVax in mosquitoes following oral exposure compared to RVFV strains MP-12 and ZH501. Infection and dissemination profiles were also measured in mosquitoes 7 days after they fed on goats inoculated with DDvax or MP-12. We hypothesized that DDVax would infect mosquitoes at significantly lower rates than other RVFV strains and, due to lack of NSm, be transmission incompetent. Exposure of Ae. aegypti and Cx. tarsalis to 8 log₁₀ plaque forming units (PFU)/ml DDVax by artificial bloodmeal resulted in significantly reduced DDVax infection rates in mosquito bodies compared to controls. Plaque assays indicated negligible transmission of infectious DDVax in Cx. tarsalis saliva (1/140 sampled) and none in Ae. aegypti saliva (0/120). Serum from goats inoculated with DDVax or MP-12 did not harbour detectable infectious virus by plaque assay at 1, 2 or 3 days post-inoculation. Infectious virus was, however, recovered from Aedes and Culex bodies that fed on goats vaccinated with MP-12 (13.8% and 4.6%, respectively), but strikingly, DDvax-positive mosquito bodies were greatly reduced (4%, and 0%, respectively). Furthermore, DDVax did not disseminate to legs/wings in any of the goat-fed mosquitoes. Collectively, these results are consistent with a beneficial environmental safety profile.

Borrelia miyamotoi strain LB-2001 retains plasmids and infectious phenotype throughout continuous culture passages as evaluated by multiplex PCR

Borrelia miyamotoi is a tick-borne spirochete of the relapsing fever borrelia group and an emerging pathogen of public health significance. The genomes of relapsing fever borreliae and Lyme disease borreliae consist of multiple linear and circular plasmids in addition to the chromosome. Previous work with B. burgdorferi sensu lato found diminished infectivity upon continuous in vitro culture passage that was attributable to plasmid loss. The effect of long-term culture passage on B. miyamotoi is not known. We generated a series of plasmid-specific primer sets and developed a multiplex PCR assay to detect the 14 known plasmids of B. miyamotoi North American strains LB-2001 and CT13-2396. We assessed the plasmid content of B. miyamotoi LB-2001 over 64 culture passages spanning 15 months and determined that strain LB-2001 retained all plasmids upon prolonged in vitro cultivation and remained infectious in mice. We also found that strain LB-2001 lacks plasmid lp20-1 which is present in strain CT13-2396. These results suggest that B. miyamotoi remains genetically stable when cultured and passaged in vitro.

Characterization of a Borrelia miyamotoi membrane antigen (BmaA) for serodiagnosis of Borrelia miyamotoi disease

Borrelia miyamotoi is a tick-borne pathogen that causes Borrelia miyamotoi disease (BMD), an emerging infectious disease of increasing public health significance. B. miyamotoi is transmitted by the same tick vector (Ixodes spp.) as B. burgdorferi sensu lato (s.l.), the causative agent of Lyme disease, therefore laboratory assays to differentiate BMD from Lyme disease are needed to avoid misdiagnoses and for disease confirmation. We previously performed a global immunoproteomic analysis of the murine host antibody response against B. miyamotoi infection to discover antigens that could serologically distinguish the two infections. An initial assessment identified a putative lipoprotein antigen, here termed BmaA, as a promising candidate to augment current research-based serological assays. In this study, we show that BmaA is an outer surface-associated protein by its susceptibility to protease digestion. Synthesis of BmaA in culture was independent of temperature at either 23 °C or 34 °C. The BmaA gene is present in two identical loci harbored on separate plasmids in North American strains LB-2001 and CT13-2396. bmaA-like sequences are present in other B. miyamotoi strains and relapsing fever borrelia as multicopy genes and as paralogous or orthologous gene families. IgM and IgG antibodies in pooled serum from BMD patients reacted with native BmaA fractionated by 2-dimensional gel electrophoresis and identified by mass spectrometry. IgG against recombinant BmaA was detected in 4 of 5 BMD patient serum samples as compared with 1 of 23 serum samples collected from patients with various stages of Lyme disease. Human anti-B. turicatae serum did not seroreact with recombinant BmaA suggesting a role as a species-specific diagnostic antigen. These results demonstrated that BmaA elicits a human host antibody response during B. miyamotoi infection but not in a tested group of B. burgdorferi-infected Lyme disease patients, thereby providing a potentially useful addition for developing BMD serodiagnostic tests.

Effectiveness of different corn dried distillers grains with solubles feeding strategies and increasing the time intervals between the second Improvest dose and slaughter of immunologically castrated pigs on belly and pork fat quality

Effects of dried distillers grains with solubles (DDGS) feeding strategies (a corn-soybean meal (CS) fed continously; CS+40% DDGS fed continously; CS+40, 30, 20, or 10% DDGS in 4 phases, respectively; or CS+40% DDGS in phases 1 to 3 and CS in phase 4 before slaughter) on belly and pork fat quality of immunologically castrated (n=192) pigs were evaluated. All pigs received the first Improvest dose at 11week of age, and the second dose at 9, 7, or 5week before slaughter at 24week of age. Increasing the time interval of the second Improvest dose before slaughter reduced IV in all fat depots and increased belly thickness. Gradually decreasing dietary DDGS and DDGS withdrawal feeding strategies reduced IV in all fat depots. Calculated IV were greater using the Meadus et al. (2010) equation compared with using the AOCS (1998) equation because it includes more long-chain unsaturated fatty acids.

Effect of time interval between the second Improvest® dose and slaughter and corn dried distillers grains with solubles feeding strategies on carcass composition, primal cutout, and pork quality of immunologically castrated pigs

Effects of dried distillers grains with solubles (DDGS) feeding strategies on carcass composition, primal cutout, and lean quality of immunologically castrated (IC; n=863) pigs were evaluated, and consisted of: 1) corn-soybean meal (CS) diet (PCon); 2) CS+40% DDGS (NCon); 3) CS+40, 30, 20, or 10% DDGS fed in phases 1 to 4, respectively (SD); or 4) CS+40% DDGS fed in phase 1 to 3 and CS in phase 4 (WD). All pigs received the first dose of Improvest® at 11weeks. of age, and the second dose was administered at either 9, 7, or 5weeks. before slaughter at 24weeks. of age. The SD and WD improved carcass dressing percentage and resulted in intermediate primal cut yields and pork loin quality compared with pigs fed PCon and NCon. Increasing the time interval between second dose of Improvest® and slaughter increased adipose tissue accretion but did not affect lean quality of pork.

Comparative vertical transmission of Rickettsia by Dermacentor variabilis and Amblyomma maculatum

The geographical overlap of multiple Rickettsia and tick species coincides with the molecular detection of a variety of rickettsial agents in what may be novel tick hosts. However, little is known concerning transmissibility of rickettsial species by various tick hosts. To examine the vertical transmission potential between select tick and rickettsial species, two sympatric species of ticks, Dermacentor variabilis and Amblyomma maculatum, were exposed to five different rickettsial species, including Rickettsia rickettsii, Rickettsia parkeri, Rickettsia montanensis, Rickettsia amblyommatis, or flea-borne Rickettsia felis. Fitness-related metrics including engorgement weight, egg production index, nutrient index, and egg hatch percentage were then assessed. Subsamples of egg clutches and unfed larvae, nymphs, and adults for each cohort were assessed for transovarial and transstadial transmission of rickettsiae by qPCR. Rickettsial exposure had a minimal fitness effect in D. variabilis and transovarial transmission was observed for all groups except R. rickettsii. In contrast, rickettsial exposure negatively influenced A. maculatum fitness and transovarial transmission of rickettsiae was demonstrated only for R. amblyommatis- and R. parkeri-exposed ticks. Sustained maintenance of rickettsiae via transstadial transmission was diminished from F₁ larvae to F₁ adults in both tick species. The findings of this study suggest transovarial transmission specificity may not be tick species dependent, and sustained vertical transmission is not common.

Growth performance of immunologically castrated pigs slaughtered at 5, 7, or 9 weeks after the second Improvest dose and fed diets containing corn dried distillers grains with solubles

Growth performance of immunologically castrated (IC) pigs (863 total) was determined at increasing time intervals between the second Improvest (gonadotropin releasing factor analog-diphtheria toxoid conjugate; Zoetis Inc., Florham Park, NJ) dose and slaughter (TD) and with 4 different dried distillers grains with solubles (DDGS) feeding strategies (FS) in a 4 × 3 factorial arrangement of treatments. The feeding period was divided into 4 separate diet phases. Dietary treatments included 1) corn-soybean meal control diets (PCon), 2) a gradual decrease of dietary DDGS inclusion rate from 40%, 30%, 20%, and 10% in phases 1 to 4 (GD), respectively, 3) feeding 40% DDGS diets in phases 1 to 3 and removal of DDGS from the phase 4 diet (WD), and 4) feeding 40% DDGS diets in all 4 phases (NCon). Pigs received the second Improvest dose at 9 (TD9), 7 (TD7), or 5 (TD5) wk before slaughter. In each group, all pigs were slaughtered on the same day. There were no 3-way interactions among FS, TD, and week of feeding period for any measure of growth performance. Pigs fed PCon and WD had greater ( < 0.05) overall ADFI than pigs fed NCon, especially when slaughtered 9 wk after the second Improvest dose (2.45 and 2.44 vs. 2.31 ± 0.08 kg/d, respectively). This response was partly due to withdrawing DDGS from the diet at 19 wk of age (WD), which led to a tendency ( < 0.10) for increased ADFI from the wk 19 to 21 interval to the wk 21 to 24 interval (3.26 vs. 3.51 ± 0.09 kg/d, respectively). During the same time period, ADFI was unchanged ( > 0.05) in pigs fed PCon, GD, and NCon. Overall G:F was improved ( < 0.05) in TD5 pigs compared with TD9 pigs and tended ( < 0.10) to be improved compared with TD7 pigs. Final BW was similar among pigs fed GD, WD, and PCon (123.1, 122.3, and 125.3 kg, respectively), but pigs fed PCon and GD had greater ( < 0.05) BW than pigs fed NCon (120.0 kg). Throughout the growing-finishing period, BW was similar among TD treatments. The GD FS was more effective than the WD FS in maintaining overall G:F (0.424 and 0.414 ± 0.005, respectively) and ADG (0.94 and 0.93 ± 0.03 kg/d, respectively), which were similar ( > 0.05) to those of pigs fed PCon (0.427 ± 0.005 and 0.96 ± 0.03 kg/d, respectively). Growth performance of pigs fed GD more closely reflected that of pigs fed PCon than that of pigs fed WD. Delaying the second dose of Improvest from 9 to 5 wk before slaughter resulted in improved growth performance.

Effect of Amblyomma maculatum (Acari: Ixodidae) Saliva on the Acute Cutaneous Immune Response to Rickettsia parkeri Infection in a Murine Model

Rickettsia parkeri Luckman (Rickettsiales: Rickettsiaceae) is a pathogenic spotted fever group Rickettsia transmitted by Amblyomma maculatum Koch (Acari: Ixodidae) in the United States. The acute innate immune response to this pathogen and the effect of tick feeding or salivary components on this response is largely unknown. We hypothesized that A. maculatum saliva enhances R. parkeri infection via downregulation of the acute cellular and cytokine immune response. C3H/HeN mice were intradermally inoculated with R. parkeri both with and without A. maculatum saliva. Flow cytometry and microscopic evaluation of inoculation site skin suspensions revealed that neutrophils and macrophages predominated at 6 and 24 h post R. parkeri inoculation, respectively. This cellular influx was significantly downregulated when A. maculatum saliva was inoculated along with R. parkeri Inflammatory cytokines (interferon γ and interleukins 6 and 10) were significantly elevated after R. parkeri inoculation. However, cytokine concentration and rickettsial load were not significantly modified by A. maculatum saliva during the acute phase of infection. These results revealed that tick saliva inhibits the cutaneous cellular influx during the acute phase of rickettsial infection. Further study is needed to determine the overall impact of this effect on the establishment of rickettsiosis in the host and development of disease.

Impact of maternal physical activity during gestation on porcine fetal, neonatal, and adolescent ovarian development

To determine how exercise from mid to late (days 40-104) gestation impacts offspring body, uterine and ovarian weight, and ovarian cell proliferation at three different developmental stages, Yorkshire gilts were either exercised by walking (EX) or not exercised (CON). In parity 1, ovaries and uteri were collected from the heaviest (H) and lightest (L) neonates and adolescent (6 mo) offspring. In parity 2, mothers were assigned the same treatment groups, and ovaries and uteri were collected from H and L fetuses on day 94 of gestation. Body weight was greater (P < 0.02) for H than L fetuses and neonates but not affected by EX treatment at any developmental stage. Ovarian weight in L but not H neonates was greater (P < 0.02) in EX than CON. Labeling index (LI; percentage of proliferating cells) was greater (P < 0.01) in cortex than medulla regions of fetal and neonatal ovaries. In fetal ovaries, EX enhanced LI (P < 0.01), and LI was greater (P < 0.01) in H compared with L offspring. In adolescent ovaries, LI was greatest (P < 0.01) in healthy antral and least in atretic antral follicles, and LI was greater (P < 0.01) in granulosa than theca cells of healthy antral follicles. Thus, exercise increased LI in fetal but not neonatal or adolescent ovaries. Although maternal exercise during gestation influences fetal and neonatal ovarian development, impacts on fertility remain unknown.

Effects of pea chips on pig performance, carcass quality and composition, and palatability of pork

Pea chips are produced as a by-product when field peas are processed to produce split peas for human consumption. The objective of this experiment was to test the hypothesis that inclusion of pea chips in diets fed to finishing pigs does not negatively influence pig growth performance, carcass composition, and the palatability of pork. A total of 24 barrows (initial BW: 58.0 ± 6.6 kg) were allotted to 1 of 4 treatments and fed early finishing diets for 35 d and late finishing diets for 35 d. A corn-soybean meal (SBM) control diet and 3 diets containing pea chips were formulated for each phase. Pea chips replaced 33.3, 66.6, or 100% of the SBM in the control diet. Pigs were housed individually, and all pigs were slaughtered at the conclusion of the experiment. Overall, there were no differences (P > 0.11) in final BW, ADFI, and G:F of pigs among treatments, but there was a quadratic response in ADG (P = 0.04), with the smallest value observed in pigs fed the control diet. Dressing percentage linearly decreased (P = 0.04) as pea chips replaced SBM in diets, but there were no differences (P > 0.20) among treatments in HCW, LM area, 10th-rib backfat, lean meat percentage, and marbling. Likewise, pH in loin and ham, drip loss, and purge loss were not influenced (P > 0.13) by treatment. However, there was a quadratic response (P = 0.08) in 24-h pH in the shoulder, with the smallest value present in pigs fed the diet, in which 66.6% of the SBM was replaced by pea chips. Subjective LM color and Japanese color score standard were reduced (quadratic, P = 0.03 and 0.05, respectively) and LM b* values and hue angle were increased (quadratic, P = 0.09 and 0.10, respectively) when pea chips replaced SBM in the diets. Ham L* (quadratic, P = 0.04), a* (linear, P = 0.02), b* (quadratic, P = 0.07), color saturation (linear, P = 0.02), and hue angle (quadratic, P = 0.05) were increased when pea chips replaced SBM. However, there were no differences (P > 0.16) in shoulder and fat color. Moreover, cook loss percentage, shear force, juiciness, and pork flavor of pork chops were not different (P > 0.10) among treatments, but tenderness of pork chops linearly decreased (P = 0.04) as SBM replaced pea chips. It is concluded that all the SBM in diets fed to growing-finishing pigs may be replaced by pea chips without negatively influencing growth performance or carcass composition. However, pigs fed pea chips will have pork chops and hams that are lighter, and chops may be less tender if pigs are fed pea chips rather than corn and SBM.

Retrospective investigation of sudden maternal weight loss as an indicator of impending parturition in the term gravida: a pilot study

The aim of the study was to perform a retrospective review of records to test a possible significant association between sudden, modest weight loss (≤2 lb) between the last two prenatal appointments in the late 3rd trimester and onset of labour. Hospital and clinic records were searched for women who delivered a term baby after the onset of natural labour between 2006 and 2008, in Tulsa, OK. High-risk pregnancies were excluded. Patients were categorised by whether they lost or gained weight between their last two prenatal appointments. The groups' average times to onset of spontaneous labour were compared. A total of 149 records were obtained. Mothers who lost weight had an average onset of spontaneous labour in 2.30 days; their counterparts' average was 2.34 days. Student's t-test and Wilcoxon test p values were 0.95 and 0.61, respectively. A Kolmogorov-Smirnov test p value was 0.2139. A one-half standard deviation difference in time to delivery, approximately 2.5 days, was detectable with 0.95 probability. It was concluded that these data may be the first time this question has been investigated and provide evidence that sudden, modest weight loss at the end of pregnancy is not associated with shorter time to onset of natural labour.

Focal liver disease: comparison of breath-hold T1-weighted MP-GRE MR imaging and contrast-enhanced CT--lesion detection, localization, and characterization

PURPOSE

To compare breath-hold T1-weighted magnetization-prepared gradient-echo (MP-GRE) magnetic resonance (MR) imaging with contrast material-enhanced computed tomography (CT) in the assessment of focal liver disease.

MATERIALS AND METHODS

The MR and CT images obtained in 64 patients with focal liver disease were reviewed by six independent reviewers in a randomized, blinded fashion. Sets of axial T1-weighted MP-GRE images, three-plane (a compilation of axial, sagittal, and coronal) T1-weighted MP-GRE images, and contrast-enhanced CT scans were analyzed. T2-weighted spin-echo (SE) MR images were also compared with CT scans.

RESULTS

Lesions were detected, localized, and characterized more accurately and generally with greater confidence with three-plane T1-weighted MP-GRE imaging than with CT (P < .01). Axial T1-weighted MP-GRE imaging was also superior (P < .05) to CT (although slightly less superior than three-plane imaging) except in the characterization of specific lesions, where both techniques were equal. T2-weighted SE MR imaging and CT were about equal.

CONCLUSION

Lesion detection, localization, and characterization are performed more accurately and confidently with breath-hold T1-weighted MP-GRE imaging than with contrast-enhanced CT, particularly when breath-hold images are obtained in three planes.

MR imaging of the liver: breath-hold T1-weighted MP-GRE compared with conventional T2-weighted SE imaging--lesion detection, localization, and characterization

PURPOSE

To compare breath-hold T1-weighted magnetization-prepared gradient-echo (MP-GRE) imaging with conventional T2-weighted spin-echo (SE) imaging in evaluation of focal liver disease.

MATERIALS AND METHODS

Images of 68 patients evaluated for focal liver disease were reviewed. Five sets of images were analyzed: axial, sagittal, and coronal breath-hold T1-weighted MP-GRE images, axial T2-weighted SE images, and a compilation of axial, sagittal, and coronal (three-plane) T1-weighted MP-GRE images. Lesion signal intensity (SI) and signal difference-to-noise (SD/N) ratios were calculated.

RESULTS

Lesions were detected, localized, and characterize more accurately (P < .05-.001) and with greater confidence on three-plane T1-weighted MP-GRE images than on almost all single-plane images. Mean SI ratios of nonsolid and solid lesions on MP-GRE and SE images were significantly different at all lesion sizes; mean SD/N ratio was significantly different only for large lesions.

CONCLUSION

Lesion detection, localization, and characterization can be accurately and confidently performed with three-plane T1-weighted MP-GRE breath-hold imaging, potentially obviating conventional T2-weighted SE imaging.

On the calculation of reference change values, with examples from a long-term study

Reference change values (sometimes called critical differences) indicate statistically important changes between test values obtained on two occasions. They are commonly computed from the median (or mean) within-subject variance observed in repeated test measurements on a number of subjects. With this computational approach, all observed within-subject variances are assumed to be estimates of a constant true variance, the same for all individuals. Moreover, any possible correlation between successive values is almost always ignored. This simplified methodology differs from the method originally proposed for computing reference change values, which accounts for variability in true variances and for serial correlation. From data obtained from repeated measurements over 2 to 5 years in 72 physically healthy subjects, we computed and compared reference change values in 18 serum analytes, using the simplified method and the originally proposed procedure. Although the original method is more complicated and requires a computer program, we believe that it produces more-reliable reference change values than those obtained by the simplified approach. The former are generally larger, but remain sensitive to clinically important changes in the individual.

On the calculation of reference change values, with examples from a long-term study

Reference change values (sometimes called critical differences) indicate statistically important changes between test values obtained on two occasions. They are commonly computed from the median (or mean) within-subject variance observed in repeated test measurements on a number of subjects. With this computational approach, all observed within-subject variances are assumed to be estimates of a constant true variance, the same for all individuals. Moreover, any possible correlation between successive values is almost always ignored. This simplified methodology differs from the method originally proposed for computing reference change values, which accounts for variability in true variances and for serial correlation. From data obtained from repeated measurements over 2 to 5 years in 72 physically healthy subjects, we computed and compared reference change values in 18 serum analytes, using the simplified method and the originally proposed procedure. Although the original method is more complicated and requires a computer program, we believe that it produces more-reliable reference change values than those obtained by the simplified approach. The former are generally larger, but remain sensitive to clinically important changes in the individual.

Statistical criteria for separate reference intervals: race and gender groups in creatine kinase

Previously published data confirming differences in creatine kinase (EC 2.7.3.2) among various race and gender subgroups in the Los Angeles area have been re-examined with use of recently proposed statistical criteria for defining separate reference intervals. Results indicate that one criterion may be too lenient, whereas another is clearly too restrictive in suggesting the need for separate intervals. Further experience with other analytes in both large and small population samples would be helpful.

Statistical criteria for separate reference intervals: race and gender groups in creatine kinase

Previously published data confirming differences in creatine kinase (EC 2.7.3.2) among various race and gender subgroups in the Los Angeles area have been re-examined with use of recently proposed statistical criteria for defining separate reference intervals. Results indicate that one criterion may be too lenient, whereas another is clearly too restrictive in suggesting the need for separate intervals. Further experience with other analytes in both large and small population samples would be helpful.

On dividing reference data into subgroups to produce separate reference ranges

We consider statistical criteria for partitioning a reference database to obtain separate reference ranges for different subpopulations. Using general formulas relating population variances, sample sizes, and the normal deviate test for the significance of the difference between two subgroup means, we show that partitioning into separate ranges produces little reduction in between-person variability, even when the differences between means are highly significant statistically. However, when there is a clear physiological basis for distinguishing between certain subgroups, simulation studies show that partitioning may be necessary to obtain reference limits that cut off the desired proportions of low and high values in each subgroup. Guidelines based on these results are provided to help decide whether separate ranges should be obtained for a given analyte.

On dividing reference data into subgroups to produce separate reference ranges

We consider statistical criteria for partitioning a reference database to obtain separate reference ranges for different subpopulations. Using general formulas relating population variances, sample sizes, and the normal deviate test for the significance of the difference between two subgroup means, we show that partitioning into separate ranges produces little reduction in between-person variability, even when the differences between means are highly significant statistically. However, when there is a clear physiological basis for distinguishing between certain subgroups, simulation studies show that partitioning may be necessary to obtain reference limits that cut off the desired proportions of low and high values in each subgroup. Guidelines based on these results are provided to help decide whether separate ranges should be obtained for a given analyte.

Generation and application of data on biological variation in clinical chemistry

Most clinical chemical analytes vary in a random manner around a homeostatic set point. Replicate analyses of a series of specimens collected from a group of subjects allows estimation of analytical, within and between subject components of variation. The preferred experimental procedures and statistical methods for evaluation of data and analysis of variance are described; a detailed example is provided in the Appendix. The many uses of data on biological variation in clinical chemistry are reviewed, including setting analytical goals, deciding the significance of changes in serial results from an individual, evaluating the utility of conventional population-based reference values in patient management, and other applications.

Proposed goals for analytical precision and accuracy in single-point diagnostic testing. Theoretical basis and comparison with data from College of American Pathologists proficiency surveys

Expressing total analytic variance as the sum of the squares of imprecision and inaccuracy, or bias, and applying the Cotlove rule recommended by the 1976 College of American Pathologists Conference on Analytical Goals in Clinical Chemistry, namely, that analytic variance should be less than one fourth of the appropriate biological variance, I derive a rule for maximum allowable imprecision in the context of single-point diagnostic testing that takes into account the bias of the test procedure. This rule may be expressed in terms of a population-based reference range (in particular, the range of test results shown in a group of healthy individuals) and the bias of the test method. The latter is required not to exceed one eighth (0.125) of the reference range. These concepts are applied to eight common analytes for which estimates of the biases of specific methods and of within-laboratory imprecision have been published for large numbers of laboratories participating in recent College of American Pathologists proficiency surveys. Results indicate that some methods widely used in 1978 fail to meet the minimum accuracy criterion, while others show negligible bias. Even neglecting bias, more recent data show that average within-laboratory imprecision is still too high for sodium, chloride, and calcium but acceptable for potassium, glucose, cholesterol, urea, and uric acid.

On the interpretation of serial laboratory measurements in acute myocardial infarction

Serial laboratory determinations are now routinely performed on patients admitted to intensive-care units. Adequate interpretation of such cumulative information for clinical decision-making purposes is a challenging problem. We describe a statistical method for predicting--sequentially as the data become available--the patient's outcome, death or survival. Thus, the method goes beyond previously reported techniques that base such prediction on only a single multivariate observation. The method has been applied to daily measurements of serum urea and lactate dehydrogenase, performed during one week on patients hospitalized in the coronary-care unit with acute myocardial infarction. Two baseline variables were also included in the dynamic risk index so derived: the age of the patient and the number of previous myocardial infarctions recorded on admission. We also discuss the problems of selecting the most-predictive laboratory tests and of determining for each test the amount of past data needed to achieve satisfactory prediction. We distinguish between global evaluation of the dynamic risk index obtained (in terms of specificity and sensitivity) and individual interpretation (in terms of posterior/prior probability ratio) of a given risk score for a particular patient. The approach described may contribute to more effective use of results of repeated laboratory tests on critically ill patients.

On the interpretation of serial laboratory measurements in acute myocardial infarction

Serial laboratory determinations are now routinely performed on patients admitted to intensive-care units. Adequate interpretation of such cumulative information for clinical decision-making purposes is a challenging problem. We describe a statistical method for predicting--sequentially as the data become available--the patient's outcome, death or survival. Thus, the method goes beyond previously reported techniques that base such prediction on only a single multivariate observation. The method has been applied to daily measurements of serum urea and lactate dehydrogenase, performed during one week on patients hospitalized in the coronary-care unit with acute myocardial infarction. Two baseline variables were also included in the dynamic risk index so derived: the age of the patient and the number of previous myocardial infarctions recorded on admission. We also discuss the problems of selecting the most-predictive laboratory tests and of determining for each test the amount of past data needed to achieve satisfactory prediction. We distinguish between global evaluation of the dynamic risk index obtained (in terms of specificity and sensitivity) and individual interpretation (in terms of posterior/prior probability ratio) of a given risk score for a particular patient. The approach described may contribute to more effective use of results of repeated laboratory tests on critically ill patients.

On the calculation of a "reference change" for comparing two consecutive measurements

We describe a statistical method for calculating a "reference change," defined as that difference between two consecutive test results in an individual that is statistically significant in a given proportion of all similar persons. By allowing for variation in within-person variances, this procedure computes a reference change that is more specific (i.e., less prone to false positives) than that obtained directly from the distribution of observed differences between measurements. Moreover, the method may easily be extended to a test for trend in three successive measurements. The method has been applied to semi-annual measurements of serum calcium and alkaline phosphatase in 698 men and women enrolled in a large health-maintenance program. We believe that these ideas may also be usefully applied to successive laboratory tests in carefully defined patient populations--but this introduces special problems, which are discussed briefly.

On the calculation of a "reference change" for comparing two consecutive measurements

We describe a statistical method for calculating a "reference change," defined as that difference between two consecutive test results in an individual that is statistically significant in a given proportion of all similar persons. By allowing for variation in within-person variances, this procedure computes a reference change that is more specific (i.e., less prone to false positives) than that obtained directly from the distribution of observed differences between measurements. Moreover, the method may easily be extended to a test for trend in three successive measurements. The method has been applied to semi-annual measurements of serum calcium and alkaline phosphatase in 698 men and women enrolled in a large health-maintenance program. We believe that these ideas may also be usefully applied to successive laboratory tests in carefully defined patient populations--but this introduces special problems, which are discussed briefly.

Comparing multivariate and univariate subject-specific reference regions for blood constituents in healthy persons

We examined the comparative behavior of subject-specific multivariate and univariate reference regions, using both computer-generated data and serial (semi-annual) measurements of selected analytes in subjects from a large health-maintenance program. Univariate studies under both homeostatic and random-walk time-series models were helpful in defining expected results, but only the homeostatic model was used in multivariate as well as univariate forms. Analysis of the computer-generated data and the real biochemical series produced similar findings, which showed the multivariate subject-specific reference region to be much more conservative than corresponding univariate intervals. That is, a multidimensional point of p correlated observations is quite likely to lie within the individual's multivariate reference region (based on past observation vectors), even when one or more of the observations lie outside their separate reference intervals for that individual. One consequence of this high specificity against univariate false positives in a large surveillance program is a higher than expected proportion of positive multivariate vectors in which none of the values lie outside their univariate ranges. Thus, although the development of multivariate reference regions should be encouraged, they should be used in conjunction with, not instead of, univariate ranges.

Comparing multivariate and univariate subject-specific reference regions for blood constituents in healthy persons

We examined the comparative behavior of subject-specific multivariate and univariate reference regions, using both computer-generated data and serial (semi-annual) measurements of selected analytes in subjects from a large health-maintenance program. Univariate studies under both homeostatic and random-walk time-series models were helpful in defining expected results, but only the homeostatic model was used in multivariate as well as univariate forms. Analysis of the computer-generated data and the real biochemical series produced similar findings, which showed the multivariate subject-specific reference region to be much more conservative than corresponding univariate intervals. That is, a multidimensional point of p correlated observations is quite likely to lie within the individual's multivariate reference region (based on past observation vectors), even when one or more of the observations lie outside their separate reference intervals for that individual. One consequence of this high specificity against univariate false positives in a large surveillance program is a higher than expected proportion of positive multivariate vectors in which none of the values lie outside their univariate ranges. Thus, although the development of multivariate reference regions should be encouraged, they should be used in conjunction with, not instead of, univariate ranges.

Statistical principles underlying analytic goal-setting in clinical chemistry

The Survey programs of the College of American Pathologists (CAP) have assessed current levels of analytic variance in many biochemical measurements, and a number of clinical chemists have proposed analytic goals. The practical importance of further reductions in analytic variance depends on the specific use of the laboratory test. Three general areas of application are described: 1) surveying a population to detect disease, 2) determining whether a particular individual's level of a given analyte is above or below a predefined alarm point, 3) monitoring an individual over a period of time to detect trends. Within each of these different contests, statistical methods are proposed for judging the practical effect of improvements in current levels of analytic precision, taking into account recent estimates of biological variation within the average individual and between individuals. As might be expected, reductions in analytic variance have greatest impact in those applications where biological variance is minimal. Such reductions will generally have little effect on the efficiency of a population survey but may be extremely valuable in decision-making concerning a particular hospital patient.

Temporal changes in the concentrations of serum constituents in healthy men. Distributions of within-person variances and their relevance to the interpretation of differences between successive measurements

The distributions of within-person variances in the concentrations of 10 commonly assayed serum constituents have been derived from data on 37 healthy male subjects studied at weekly intervals over a period of five months. All 10 distributions appear to be of log-normal form. The relevance of the findings to the interpretation of differences between serial measurements in a given individual is discussed. Examples are given to show how the information on within-person variances for a particular analyte, organised into a simple graph, may be used to test medical opinions on threshold values for serial changes in the concentration of this analyte in a given individual. In this way, biological variability as well as analytical error may be taken into account quantitatively when assessing the significance of a difference between two serial measurements.

Gallium-67 citrate scanning in the staging of idiopathic pulmonary fibrosis: Correlation and physiologic and morphologic features and bronchoalveolar lavage

Idiopathic pulmonary fibrosis is a fatal disorder characterized by interstitial fibrosis and parenchymal inflammation. Current concepts of this disease suggest that the inflammation precedes and probably induces the fibrotic state. To evaluate the extent and relative activity of the inflammatory process, we scanned patients with idiopathic pulmonary fibrosis using gallium-67, a radionuclide known to concentrate in regions of inflammation. To quantify the amount of isotope in the lung parenchyma, the 67Ga-index was developed, a parameter derived from estimates of the size of regional pulmonary uptake, the uptake intensity, and its texture. Evaluation of 67Ga scans in 30 patients with idiopathic pulmonary fibrosis and 19 control subjects demonstrated that the 67Ga-index in the group with idiopathic pulmonary fibrosis was significantly higher (P less than 0.001) than that in the control group. When compared with lung biopsy morphologic studies in 22 patients with idiopathic pulmonary fibrosis, the 67Ga-index correlated with the degree of interstitial cellularity (P less than 0.05) and the degree of alveolar cellularity (P less than 0.005). When compared with cellular analysis of bronchoalveolar lavage fluid in 17 patients with idiopathic pulmonary fibrosis, the 67Ga-index correlated with the differential percentage of neutrophils (P less than 0.05), but not lymphocytes, eosinophils, or macrophages. These studies indicate that 67Ga accumulates in the lungs of patients with idiopathic pulmonary fibrosis and is probably associated with the active inflammatory state. The associations of the 67Ga-index with morphologic features and bronchoalveolar lavage analysis suggest that quantitative evaluation of these scans may be useful in staging the activity of idiopathic pulmonary fibrosis and following responses to therapy.

Intra-individual variation of some serum constituents and its relevance to population-based reference ranges

The advent of high-capacity multi-channel analyzers allows estimation of long-term variability in serum constituents of large numbers of subjects. By frozen storage of specimens with subsequent analysis in a single machine run, long-term analytical variation may be eliminated, thus sharpening the estimates of intra-individual variation. In the present study we used the Vickers M-300 analyzer to obtain the data for such estimates from 37 male volunteers, each bled once a week for 22 weeks. Secimens were analyzed in random order to eliminate any biasing effect of analytical drift during the 4-h machine run. Ten serum constituents were measured. Storage-induced linear trends were small or negligible during the period of specimen collection. Using the ratio of average within-subject variance to the variance among subjects as a guide, serum alkaline phosphatase was found to show the greatest individuality, sodium and potassium the least. Other constitutents showed varying degrees of individuality, but for all these analytes, the usual population-based reference ranges were found to be either insensitive or irrelevant to the study of concentration changes over time within most healthy subjects. Our results generally confirmed those of smaller but comparable earlier studies.

Intra-individual variation of some serum constituents and its relevance to population-based reference ranges

The advent of high-capacity multi-channel analyzers allows estimation of long-term variability in serum constituents of large numbers of subjects. By frozen storage of specimens with subsequent analysis in a single machine run, long-term analytical variation may be eliminated, thus sharpening the estimates of intra-individual variation. In the present study we used the Vickers M-300 analyzer to obtain the data for such estimates from 37 male volunteers, each bled once a week for 22 weeks. Secimens were analyzed in random order to eliminate any biasing effect of analytical drift during the 4-h machine run. Ten serum constituents were measured. Storage-induced linear trends were small or negligible during the period of specimen collection. Using the ratio of average within-subject variance to the variance among subjects as a guide, serum alkaline phosphatase was found to show the greatest individuality, sodium and potassium the least. Other constitutents showed varying degrees of individuality, but for all these analytes, the usual population-based reference ranges were found to be either insensitive or irrelevant to the study of concentration changes over time within most healthy subjects. Our results generally confirmed those of smaller but comparable earlier studies.

Comparison of estimates of long-term analytical variation derived from subject samples and control serum

Variation in the assays of uniform control serum commonly are assumed to represent day-to-day analytical variation. To test this assumption, we compared the differences between results of serum aliquots assayed immediately for 12 constituents and frozen aliquots accumulated and assayed on a single day with the results of control serum variation from the same period. One aliquot of each weekly sample was stored frozen. Eleven subjects were sampled for 12 weeks. Storage at --20 degrees C for 15 weeks had a mild destructive effect on two enzymes in serum. The control serum data revealed significant linear trends in magnesium (upwards) and alkaline phosphatase (downwards) that substantially increased the respective variances. In the other 10 constituents tested, comparison of variances indicated that long-term (weeks) variation in control serum assays is similar to the difference of variation between aliquots assayed immediately and those frozen and assayed at the same time. For these constituents, this finding justifies the use of control serum to estimate long term analytical variation.

Comparison of estimates of long-term analytical variation derived from subject samples and control serum

Variation in the assays of uniform control serum commonly are assumed to represent day-to-day analytical variation. To test this assumption, we compared the differences between results of serum aliquots assayed immediately for 12 constituents and frozen aliquots accumulated and assayed on a single day with the results of control serum variation from the same period. One aliquot of each weekly sample was stored frozen. Eleven subjects were sampled for 12 weeks. Storage at --20 degrees C for 15 weeks had a mild destructive effect on two enzymes in serum. The control serum data revealed significant linear trends in magnesium (upwards) and alkaline phosphatase (downwards) that substantially increased the respective variances. In the other 10 constituents tested, comparison of variances indicated that long-term (weeks) variation in control serum assays is similar to the difference of variation between aliquots assayed immediately and those frozen and assayed at the same time. For these constituents, this finding justifies the use of control serum to estimate long term analytical variation.