Enteric disease surveillance under the AFHSC-GEIS: current efforts, landscape analysis and vision forward

The mission of the Armed Forces Health Surveillance Center, Division of Global Emerging Infections Surveillance and Response System (AFHSC-GEIS) is to support global public health and to counter infectious disease threats to the United States Armed Forces, including newly identified agents or those increasing in incidence. Enteric diseases are a growing threat to U.S. forces, which must be ready to deploy to austere environments where the risk of exposure to enteropathogens may be significant and where routine prevention efforts may be impractical. In this report, the authors review the recent activities of AFHSC-GEIS partner laboratories in regards to enteric disease surveillance, prevention and response. Each partner identified recent accomplishments, including support for regional networks. AFHSC/GEIS partners also completed a Strengths, Weaknesses, Opportunities and Threats (SWOT) survey as part of a landscape analysis of global enteric surveillance efforts. The current strengths of this network include excellent laboratory infrastructure, equipment and personnel that provide the opportunity for high-quality epidemiological studies and test platforms for point-of-care diagnostics. Weaknesses include inconsistent guidance and a splintered reporting system that hampers the comparison of data across regions or longitudinally. The newly chartered Enterics Surveillance Steering Committee (ESSC) is intended to provide clear mission guidance, a structured project review process, and central data management and analysis in support of rationally directed enteric disease surveillance efforts.

Screening for syphilis infection in pregnant women: evidence for the U.S. Preventive Services Task Force reaffirmation recommendation statement

BACKGROUND

In 2004, the U.S. Preventive Services Task Force strongly recommended that clinicians screen all pregnant women for syphilis infection.

PURPOSE

To update the evidence on screening pregnant women for syphilis infection.

DATA SOURCES

MEDLINE searches from 1 January 2003 through 31 July 2008, recent systematic reviews, reference lists of retrieved articles, and expert suggestions.

STUDY SELECTION

English-language studies were selected to answer the following 2 questions: Does screening for syphilis in pregnancy reduce the prevalence of congenital syphilis in neonates? Are there harms of screening for syphilis or harms of treatment with penicillin in pregnancy to women or neonates? Randomized, controlled trials; meta-analyses; systematic reviews; cohort studies; and ecologic studies were selected for the potential benefits question. Randomized, controlled trials; meta-analyses; systematic reviews; cohort studies; case-control studies; and large case series were selected for the potential harms question.

DATA EXTRACTION

Information on the study design, selection criteria, demographic characteristics, and clinical outcomes was extracted from each study.

DATA SYNTHESIS

One study on benefits evaluated the effect before and after the implementation of a universal syphilis screening program for pregnant women and found reductions in rates of congenital syphilis. Two studies on screening accuracy for syphilis reported false-positive rates of less than 1%. One study that used a large insurance claims database reported an incidence of anaphylaxis after oral penicillin of 0.1 per 10,000 dispensings. In a study from Hungary, oral penicillin in pregnancy was not associated with orofacial clefts.

LIMITATIONS

This was a targeted literature search and could have missed small studies on the benefits and harms of screening for syphilis in pregnancy. We did not review evidence on interventions to improve rates of prenatal screening.

CONCLUSION

New evidence from a study of universal screening supports previous evidence on the effectiveness of screening for syphilis in pregnancy to prevent congenital syphilis. Harms include testing and follow-up for false-positive test results and adverse effects from penicillin treatment.

Regulation of adrenal atrial natriuretic hormone receptor subtypes

Regulation of atrial natriuretic hormone (ANH) receptor binding and aldosterone suppression was studied in isolated adrenal glomerulosa cells from rats fed a high-salt (HS) or low-salt (LS) diet for 3 days. In plasma of HS rats, aldosterone levels were 5 times lower and immunoreactive ANH two times higher than in LS rats. Competitive binding studies showed the same affinity for human atrial natriuretic hormone (hANH) in both pools of cells, but receptor density was 50% higher on LS cells. A linear ANH analog that binds to non-guanylate-cyclase-coupled receptors did not show increased binding to LS cells. Cyclic GMP production in response to hANH was identical in both groups. The aldosterone-inhibitory effect of hANH on both groups of basal and angiotensin II-stimulated cells was also identical. Thus a short-term high-salt diet causes decreased density of ANH receptors in glomerulosa cells without changing biological activity of ANH. These results suggest that dietary salt content changes the number of ANH receptors and that non-guanylate-cyclase-coupled receptors contain at least two classes of receptors.

The physiological role of atrial natriuretic hormone in the regulation of aldosterone and salt and water metabolism

To investigate the mechanisms by which small changes in plasma levels of atrial natriuretic hormone (ANH) affect aldosterone, 10 normal young men were infused for 2 h with 0.6 pmol/kg.min human [Ser,Tyr28]ANH under 3 study conditions: 1) high salt diet (H), 2) low salt diet (L), and 3) low salt diet plus pretreatment with the angiotensin-converting enzyme inhibitor enalapril (LE). Baseline ANH levels were higher on H than on L or LE. A postural drop in ANH was observed when subjects went from standing to sitting. Plasma ANH levels increased during infusion by up to 4.5 pmol/L (H, 7.0 +/- 1.3 to 11.5 +/- 1.4; L, 4.3 +/- 0.6 to 8.7 +/- 1.1; LE, 4.2 +/- 0.5 to 8.6 +/- 1.5). At all time points, plasma ANH was well within the normal range. Plasma aldosterone did not change during H, decreased by about 60% for both low salt conditions, and remained suppressed at 1 h of recovery for L, but not for LE. This suggests that ANH can suppress aldosterone by both indirect and direct mechanisms, although the indirect mechanism appears to predominate. A prompt increase in urine flow was seen during ANH infusion and was sustained at 1 h of recovery, but little change was seen in urinary sodium or potassium excretion, heart rate, or blood pressure. The difference between the natriuretic and diuretic effects of ANH was seen under all conditions. These results support the hypothesis that within the normal physiological range, ANH is a regulator of salt and water metabolism in normal man.

Developmental aspects of the renal kallikrein-like activity in fetal and newborn lambs

The ontogeny of the renal kallikrein-like activity and the interrelationships between this enzyme and the renin-angiotensin-aldosterone and prostaglandin systems were studied in 43 chronically catheterized sheep fetuses between 104 and 142 days of gestation (term, 145 days) and in 8 chronically catheterized newborn lambs between 5 and 23 days of age. Urinary kallikrein (UKall) excretion rate expressed in absolute values (mEU/hr) or corrected for kidney weight (mEU X hr-1 X gKW-1) or glomerular filtration (mEU X hr-1 X ml GFR-1) increased significantly during fetal maturation and after birth. The rise in UKall during fetal and newborn life was not dependent on an increase in urinary flow rate (r = 0.06). The increase in fetal UKall (mEU X hr-1 X gKW-1) correlated closely with the rise in plasma aldosterone concentration for values above 35 pg/ml (r = 0.72, P less than 0.001). A significant negative correlation was found between UKall (mEU X hr-1 X gKW-1) and log of individual urinary sodium excretion values (r = -0.78, P less than 0.001). No correlation was found between UKall and urinary prostaglandins (PGE, PGF2 alpha) excretion during fetal and newborn life, but UKall correlated closely with the rise in renal blood flow during maturation (r = 0.87, P less than 0.001). The present data suggest that aldosterone is an important regulator of UKall release early during development. It is also suggested that conceptional age is an important factor which may modulate the renal sensitivity to aldosterone-stimulated UKall excretion.

Metabolic effects of constant hypertonic glucose infusion in well-oxygenated fetuses

In order to investigate the metabolic effects of a constant hypertonic glucose infusion in well-oxygenated fetuses, ten experiments were carried out in nine long-term experiments in fetal lambs. It appeared that a constant hypertonic glucose infusion did not significantly affect the fetal blood gases, pH, and plasma lactate levels when fetal glucose was kept below 150 mg. per 100 ml. It was also demonstrated that glucose infusions significantly increased the fetal lactate levels and decreased the blood pH when fetal plasma glucose was over 150 mg. per 100 ml. However, there was no decrease in fetal PO2 and pco2 until fetal glucose reached values over 300 mg. per 100 ml. These studies suggest that constant hypertonic glucose infusion does not improve fetal blood gases or pH and that fetal hyperglycemia over 300 mg. per 100 ml. produces severe metabolic acidosis.

In vivo demonstration of renal carbonic anhydrase activity in the fetal lamb

The capacity of the fetal renal carbonic enzyme to facilitate the renal reabsorption of bicarbonate was studied in 8 long-term fetal lamb preparations (103-124 days of gestation). After acetazolamide administration the fetal arterial blood pH and PCO2 values decreased significantly (p less than 0.05). Significant increases in fetal urinary pH (p less than 0.001), and urinary excretion of bicarbonate (p less than 0.001), potassium (p less than 0.05) and total cation (Na+ + K+) were observed after carbonic anhydrase inhibition. It is suggested from these in vivo studies that renal carbonic anhydrase is present and active during fetal life and does not limit the capacity of the fetal kidney to reabsorb bicarbonate.

Interrelationship between glomerular filtration rate and renal transport of sodium and chloride during fetal life

The maturation of the glomerular filtration rate (GFR) and the interrelationship between the GFR and the renal transport of sodium and chloride have been evaluated during the last trimester of gestation with the use of long-term experiments in fetal lambs. An increase in GFR (milliliters per minute) parallel to the increase in fetal body weight was demonstrated; however, no significant change was shown when the GFR (milliliters per minute per kilogram of fetal body weight) (1.141 +/- 0.079) was related to fetal body weight or gestational age. There was a constant increase in sodium and chloride reabsorption (microequivalents per minute) during the last third of gestation. This increase in sodium and chloride reabsorption was less than the increase in GFR (milliliters per minute) before 129 days but became higher than the rise of GFR (milliliters per minute) after 129 days of gestation.

Influence of fetal extracellular volume contraction on renal reabsorption of bicarbonate in fetal lambs

In order to determine the renal threshold for bicarbonate in the fetal lamb and factors that may influence renal reabsorption of bicarbonate in the fetus, 18 acute fetal lamb preparations (110-140 days of gestation) were studied. In the first series of experiments involving nine fetuses, the renal bicarbonate threshold of normal fetuses varied from 12.0 to 23.5 mM/liter with a mean value of 17.7 +/- 1.37 mM/liter. This is significantly lower (P less than 0.005) than the value measured in five adult sheep of 28.7 +/- 1.68 mM/liter. There was a significant and positive correlation between the fetal plasma bicarbonate at threshold level and the fetal kidney weight, as well as fetal age. In a second series of experiments, the excretion of bicarbonate and sodium was studied in nine fetuses before and after dehydration by peritoneal dialysis. After peritoneal dialysis there was a significant decrease in urinary pH (P less than 0.025), bicarbonate excretion (P less than 0.001), sodium excretion (P less than 0.001), fractional excretion of sodium (P less than 0.01). When glucose was replaced by mannitol in the peritoneal dialysis fluid the effects on bicarbonate reabsorption paralleled those when glucose was present in dialysis fluid. It was also shown that when glucose was given intravenously to the fetus, up to a plasma concentration of 200 mg/100 ml, there was no effect on the fetal renal reabsorption of bicarbonate. These data indicate that the low threshold for bicarbonate reabsorption by the fetal kidney is not due to a limited capacity to increase bicarbonate or sodium reabsorption and suggest that the fetal kidney is able to respond to volume depletion by increasing its reabsorption in bicarbonate and electrolytes.

Maturational changes in the fetal glomerular filtration rate

Few data are available documenting the evolution of glomerular filtration rate (GFR) during gestation. In order to investigate this aspect, 33 fetal sheep have been studied, with the use of an intrauterine fetal preparation. It appears that the actual GFR (AGFR) in milliliters per minute increased during the last third of gestation without a significant increase in GFR expressed as milliliters per minute per kilogram of fetal weight (GFR-FW) and as milliliters per minute per gram of kidney weight (GFR-KW). It is suggested that a parallel and constant increase in AGFR and in total fetal weight or kidney weight might explain the absence of variation if GFR-FW or GFR-KW during the last third of gestation.