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Biomedical subjects

L K Pickering

Publications and source records attributed to L K Pickering.

At least 55 records · Page 3Linked to original sources
PubMed1995

Virologic features of an astrovirus diarrhea outbreak in a day care center revealed by reverse transcriptase-polymerase chain reaction.

Astroviruses cause outbreaks of diarrhea in children attending day care centers (DCCs). Reverse transcriptase-polymerase chain reaction (RT-PCR) was compared with EIA detection of astrovirus in stool specimens to characterize further the molecular epidemiology of an outbreak of astrovirus-associated gastroenteritis. Three hundred sixty-eight stool specimens collected prospectively from 36 children enrolled in a DCC during an 11-week outbreak of diarrhea were evaluated by EIA and RT-PCR. Astrovirus was detected in 32% of specimens by RT-PCR versus 10% by EIA (P < .001) and in 89% of children by RT-PCR versus 50% by EIA. The median duration of astrovirus excretion episodes detected by EIA was 1.5 days versus 4 days by RT-PCR (P = .06). Astrovirus was excreted for prolonged periods by immunocompetent children during this outbreak. RT-PCR was more sensitive than EIA for detection of astrovirus in stool specimens and redefined the epidemiology of astrovirus infection in this setting.

Age Factors↗
PubMed1995

Development of an ELISA to detect MX virus, a human calicivirus in the snow Mountain agent genogroup.

MX virus is a Snow Mountain agent (SMA) genogroup human calicivirus (HuCV) identified in a Mexican child with diarrhoea. An ELISA using hyperimmune antisera to the recombinant MX virus (rMX) capsid was developed to detect SMA genogroup HuCVs in stool specimens. The rMX ELISA detected the prototype MX virus, SMA, and Hawaii agent (HA), but not Norwalk virus (NV) or Sapporo virus. Twenty-three diarrhoea stool specimens from children attending day care centres in Norfolk, Virginia, were positive by the rMX ELISA and results were confirmed by reverse transcription-polymerase chain reaction (RT-PCR). Eight of 20 diarrhoea stool specimens from children in the United Kingdom previously shown to contain small round structured viruses (SRSVs) or HuCVs by electron microscopy were also positive by the rMX ELISA and RT-PCR. Sequence analysis of the RT-PCR products showed that all the rMX ELISA-positive viruses belong to the SMA genogroup. These data also showed that the SMA genogroup can be further divided into two subgroups: subgroup 1 includes prototypes SMA and HA, and subgroup 2 includes MX virus, minireovirus, Oth-25 and Bristol virus.

Animals↗
PubMed1995

Expression, self-assembly, and antigenicity of a snow mountain agent-like calicivirus capsid protein.

Virus-like particles were produced in insect cells infected with a recombinant baculovirus containing the capsid gene of MX virus, a Mexican strain of human calicivirus. These recombinant MX (rMX) particles were morphologically similar to recombinant Norwalk virus (rNV) particles as observed under an electron microscope and contained a single capsid protein with a molecular weight of 57,000, which was slightly smaller than that of rNV. This protein was immunoprecipitated by sera from volunteers infected with the Snow Mountain agent, but it reacted weakly with sera from volunteers infected with NV. This protein did not react with hyperimmune antisera from animals immunized with rNV in the rNV antigen enzyme immunoassay (EIA). Seroresponses were detected from volunteers infected with Snow Mountain agent and Hawaii agent when the rMX particles were used as antigen in an EIA. This EIA also detected an immune response in the sera of child from whom the MX virus was isolated, and a high prevalence of antibody to MX virus was found in the sera of a cohort of Mexican children.

Animals↗
PubMed1994

Assessment of epitope-blocking assays for measuring antibody to rotavirus.

Criteria for determining the presence of antibody and of a response to infection in the epitope-blocking assay for anti-rotavirus antibody were evaluated using 222 sera from children younger than 30 months of age. The children were monitored for rotavirus diarrhea by means of daily symptom records and weekly stool specimen collection, whether or not symptoms occurred. Sera were collected at 6-month intervals. Forty-three serum pairs were collected before and after documented rotavirus infections. The remaining 136 sera were collected from children with no identified infections in the monitoring interval. Use of a 50% cutoff-point, as in prior reports, was too stringent a criterion for determining the presence of blocking antibody. The absolute percent blocking at the 1:10 serum dilution was a better measure of antibody content than end-point titration using the 50% cutoff-point.

Antibodies, Viral↗
PubMed1994

Anti-rotavirus G type-specific and isotype-specific antibodies in children with natural rotavirus infections.

Serum VP7 (G) type- and isotype-specific anti-rotavirus antibodies were assessed among children monitored longitudinally over one or two rotavirus seasons in day care centers. Seventy-five pairs of blood specimens from 63 children were tested for anti-rotavirus antibodies. Stool specimens were collected weekly and tested for rotavirus antigen. G typing of detected rotaviruses showed that seven outbreaks of G1 and one of G3 occurred during the two seasons. G type-specific responses to the outbreak strain occurred among 79% of infected children and 9% of children with infection not detected (P < .001). Of children infected with G1, 54% had a heterotypic response; they were older (P = .048) and had higher preexisting G1 antibody levels than children who had only homotypic responses (P = .012). Higher IgA, IgG, and homotypic antibody levels to the antigenic site C of the G1 and G3 VP7s correlated with protection against infection and illness, homotypic antibody independently of IgA or IgG titers.

Antibodies, Viral↗
PubMed1994

Asymptomatic Shigella infections in a cohort of Mexican children younger than two years of age.

The proportion of Shigella infections that occur asymptomatically in young children has not been established. A community-based cohort study of 367 infants was followed prospectively by weekly home visits from January, 1990, through December, 1991. Stool samples were collected weekly and when diarrhea occurred and were tested for Shigella and other enteropathogens. There were 2925 child months of observation and 65 episodes of Shigella infection. There were 3.1 episodes/100 child months during the warm season (May through September) and 0.97 episode/100 child months during the cold season. Shigella infections were rare during the first 6 months of life but increased with age (P < 0.0001). Overall 55% of detected infections were asymptomatic. The proportion of infections that were asymptomatic increased as age increased (P < 0.01). Symptom status was not significantly associated with Shigella species or season. All isolates from symptomatic and asymptomatic children had the 120- to 140-megadalton virulence plasmid. We conclude that infections with virulent strains of Shigella are commonly asymptomatic in Mexican children during the first 2 years of life.

Age Distribution↗
PubMed1994

Acquisition of serum isotype-specific and G type-specific antirotavirus antibodies among children in day care centers.

The acquisition of serum antirotavirus antibodies among children in day care centers was monitored through two rotavirus seasons. Twenty-six children were monitored daily for diarrhea and weekly for stool rotavirus excretion through a rotavirus season of infections with serotype G1 and a successive season of infections with both G1 and G3. Sera were collected before and after each rotavirus season and tested for antirotavirus IgA and IgG and for G type-specific blocking antibody. The prevalence of protective serum IgA and IgG titers increased from 36% and 45% before Season 1 to 77% and 96% after Season 2, respectively (P < 0.02 and 0.001). G type-specific antibodies also increased (G1, P < 0.001; G2, P = 0.005; G3, P = 0.003; G4, P = 0.006), including for noncirculating types. Homotypic and heterotypic antibodies increased as the number of rotavirus infections experienced by a child increased. The group of children with two proven infections developed protective isotype-specific and G type-specific antibodies. These results indicate that in first exposures to rotavirus G types, children develop predominantly homotypic antibody. However, as the number of rotavirus infections increase, children develop heterotypic antibody to G types at levels that correlate with broad protection against rotavirus infection and illness, despite exposure to a restricted number of G types.

Antibodies, Viral↗
PubMed1994

Necrotizing enterocolitis and infection.

Infections are considered to play an important role in the pathogenesis of necrotizing enterocolitis (NEC). The evidence for infectious causes of NEC is reexamined, with special attention to the clinical definition and reported outbreaks of NEC. Future areas of study are proposed.

Bacterial Infections↗
PubMed1994

Secretory anti-Giardia lamblia antibodies in human milk: protective effect against diarrhea.

OBJECTIVE: To determine whether anti-Giardia lamblia secretory IgA (sIgA) antibodies in human milk protect infants from acquisition of or symptoms associated with Giardia infection. METHODS: One hundred ninety-seven Mexican mother/infant pairs were followed weekly from birth for diarrheal disease and feeding status. Infant stool specimens were collected weekly and were cultured for bacterial pathogens and tested for Giardia and rotavirus by enzyme-linked immunosorbent assay. Maternal milk samples were collected weekly for 1 month postpartum and monthly thereafter. To determine the protective effect of anti-Giardia sIgA in milk against infection and against diarrhea due to Giardia, milk samples from mothers of infected infants and appropriately matched controls were assayed for anti-Giardia sIgA by enzyme-linked immunosorbent assay. RESULTS: Asymptomatic, infected infants ingested significantly (P = .046) higher amounts of milk anti-Giardia sIgA compared with symptomatic, infected infants. However, milk anti-Giardia sIgA concentrations did not differ between Giardia-infected and noninfected infants. CONCLUSION: The amount of anti-Giardia sIgA in human milk was associated with prevention of symptoms of diarrhea due to Giardia, but not with acquisition of the organism.

Animals↗
PubMed1993

Child day care increases the risk of clinic visits for acute diarrhea and diarrhea due to rotavirus.

A case-control study of risk factors for acute diarrhea was conducted among children under 3 years of age attending a health maintenance organization clinic in Houston, Texas. During a 19-month period from September 1985 through March 1987, 339 children with diarrhea and 363 age- and season-stratified controls were enrolled. A total of 90% of cases were under age 2 years. Compared with children cared for at home, the risk of clinic visits for diarrhea was significantly greater for children receiving child day care and was similar for those attending day care centers (odds ratio (OR) = 2.4, 95% confidence interval (CI) 1.6-3.7), day care homes (OR = 2.0, 95% CI 1.3-3.1), mother's day out (OR = 1.8, 95% CI 0.8-4.2), or when cared for by a relative (OR = 2.0, 95% CI 1.2-3.2). Rotavirus-positive diarrhea was also significantly greater in child day care (OR = 2.4, 95% CI 1.1-5.1). The day care-associated risk was highest during the first month of enrollment (OR = 3.1, 95% CI 1.8-5.4). In this population, where 40% of children receive child care, 19% of the clinic visits for acute diarrhea were attributable to child care. These data indicate that child day care increases the risk of acute diarrhea, whether in a center or in a home, and the risk is highest in the first month of enrollment.

Acute Disease↗
PubMed1993

Outbreaks of astrovirus gastroenteritis in day care centers.

OBJECTIVE: This study evaluated astrovirus as a cause of diarrhea outbreaks among infants and toddlers in day care centers. DESIGN: Stool specimens were collected weekly during four periods (from January 1986 through December 1991) from children 6 to 30 months of age who were enrolled in prospective studies of diarrhea in day care centers. All diarrheal stool specimens were tested for bacterial enteropathogens, rotavirus, enteric adenovirus, and Giardia lamblia. A total of 1365 stool specimens from 70 outbreaks in which no etiologic agent was identified and from another 11 outbreaks with a known cause were tested for astrovirus, by means of a monoclonal antibody-based enzyme immunoassay. Confirmatory testing was performed by reverse transcriptase-polymerase chain reaction with primers designed to produce an 89 base-pair product. RESULTS: Astrovirus was detected in 6 (7%) of the 81 outbreaks. Of 217 children tested, 73 (34%) were infected with astrovirus; infections in 35 (48%) were symptomatic and in 38 (52%) asymptomatic. The six outbreaks lasted 11 to 44 days (median 22 days). Astrovirus excretion was detected for a duration of 2 to 30 days, with excretion occurring from 1 to 8 days (median 2 days) before diarrhea began to 1 to 20 days (median 2 days) after diarrhea ceased. Younger children (< or = 12 months) were at greater risk than older children (p = 0.011) of becoming infected with astrovirus during an outbreak and were more likely (p = 0.015) to have symptoms when infected. Of 24 specimens with astrovirus by enzyme immunoassay, 20 (83%) were confirmed to have the virus by reverse transcriptase-polymerase chain reaction. CONCLUSION: Astrovirus was an important cause of outbreaks of diarrhea among children attending day care centers, more frequently infected younger children, and often produced asymptomatic infections.

Age Factors↗
PubMed1993

Fecal antibody responses to symptomatic and asymptomatic rotavirus infections.

The role of anti-rotavirus fecal IgA (RVflgA) in protecting children against natural rotavirus infections is unclear. Rotavirus outbreaks occurred in each of four day care centers attended by 129 children; 42% of the infections were asymptomatic. RVflgA titers were measured by EIA before infection and 4 weeks later in 50 children who excreted rotavirus (excretors) and in two samples 4 weeks apart from 50 children without detected virus excretion (nonexcretors). Forty-three (86%) excretors and 18 (36%) nonexcretors had a fourfold or greater RVflgA titer rise. Preexposure RVflgA titers were higher in not infected than symptomatic (P = .002), asymptomatic than symptomatic (P = .036), and not infected than asymptomatic children (P = .07). RVflgA titers after asymptomatic infections were slightly than after symptomatic infections (P = .087). In summary, higher RVflgA titers were associated with protection against infection and illness and increased fourfold or more in both asymptomatic and symptomatic children.

Age Factors↗
PubMed1993

Diarrhea associated with Aeromonas species in children in day care centers.

Outbreaks of diarrhea caused by enteropathogens have been reported in day care centers (DCC), but Aeromonas species have not been implicated. This study evaluated 381 children involved in 51 outbreaks in four DCC to determine the association of Aeromonas species with diarrhea and to characterize the isolates. The organism was identified in two outbreaks of diarrhea. In one, Aeromonas species were isolated from 6 (24%) of 25 children and in the other from 5 (21%) of 24 children. Seven other Aeromonas strains from children in DCC were studied. Fourteen (78%) of 18 were Aeromonas caviae and 15 were from children with diarrhea. Of the isolates, 75% did not have plasmids detected; all others had unique plasmid patterns. All strains had different DNA content. Twenty-two control isolates of Aeromonas from children with diarrhea in Mexico and Dallas had different chromosomal DNA patterns. Most Aeromonas infections were associated with symptoms. Chromosomal DNA patterns differentiated Aeromonas strains better than did plasmid DNA patterns. The outbreaks of diarrhea were unusual in that several different Aeromonas genospecies were involved in each outbreak.

Aeromonas↗
PubMed1993

Cohort study of rotavirus serotype patterns in symptomatic and asymptomatic infections in Mexican children.

A cohort of 200 Mexican children from a low income periurban community was monitored from birth to the age of 2 years to determine the serotype-specific incidence, morbidity and seasonal pattern of symptomatic and asymptomatic human rotavirus (HRV) infections. A total of 177 HRV infections occurred in 134 (67%) children; 50% of these infections were asymptomatic. The incidence of all HRV infections was 0.6 episode/child year and was inversely related to age (r = -0.93; P < 0.01). The incidence of HRV-associated diarrhea was 0.3 episode/child year, with the highest frequency and severity occurring in infants between 4 and 6 months of age. HRV infections were more frequent each autumn, with a changing sequential pattern of predominant serotypes. Overall serotype 3 (34%) was the most frequent, followed by serotypes 1 (16%), 2 (15%) and 4 (6%). The 4 serotypes were associated with a similar risk for diarrhea and severity of diarrhea. In 23 (26%) HRV diarrhea-associated infections, an additional enteropathogen was identified; these mixed infections were more frequent in older children (chi square, 4.45; P < 0.05) but were not more severe (chi square, 0.02; P > 0.05). Our data indicate that HRV infections were common early in life, seasonal, frequently asymptomatic and caused by a variety of serotypes, none of which was a risk factor for diarrhea or severity of diarrhea.

Cohort Studies↗
PubMed1993

Costs associated with office visits for diarrhea in infants and toddlers.

We determined costs associated with diarrhea in a < 36-month-old ambulatory population. Children with acute diarrhea were enrolled during the rotavirus season at three centers. Questionnaires to assess costs of both medical and nonmedical factors were administered at the enrollment visit and 1 week later. Office computer records were reviewed to identify all visits by children with diarrhea during 1 year. Fifty-one patients were enrolled. The average cost per episode of diarrhea was $289, which included: $144, missed work; $57, office visits; $23, laboratory tests; $21, medications; $18, changed diet/oral rehydration solutions; $15, travel; $7, extra diapers; and $6, extra child care. During 1 year diarrhea accounted for 4% of all visits and 10% of visits among those < 36 months old. The annual cost at the three centers was $346,000, which extrapolates to $0.6 to $1.0 billion for the United States. Twenty-one percent of this cost was attributable to rotavirus diarrhea. We conclude that outpatient care for pediatric diarrhea is a major health care cost in the United States.

Child, Preschool↗