Search

Nucleic acid amplification for the enteropathogens Cryptosporidium and Giardia is complicated by low target template concentrations and PCR inhibitors. In this work we designed dual capture oligonucleotides for both Cryptosporidium and Giardia 18S rRNA targets which when utilized during DNA extraction from stool improved the limit of detection of our multiplex PCR assay by 1-2 logs, to as little as 10 cysts. When applied to clinical specimens, the method improved the real-time PCR C(T) by an average of 10.7 ± 9.7 cycles. This work provides a highly sensitive protocol for Cryptosporidium and Giardia when limit of detection is of utmost importance.

Campylobacter is a common bacterial enteropathogen that can be detected in stool by culture, enzyme immunoassay (EIA), or PCR. We compared culture for C. jejuni/C. coli , EIA (ProSpecT), and duplex PCR to distinguish Campylobacter jejuni/C. coli and non- jejuni/coli Campylobacter on 432 diarrheal and matched control stool samples from infants in a multisite longitudinal study of enteric infections in Tanzania, Bangladesh, and Peru. The sensitivity and specificity of culture were 8.5% and 97.6%, respectively, compared with the results of EIA and 8.7% and 98.0%, respectively, compared with the results of PCR for C. jejuni/C. coli . Most (71.6%) EIA-positive samples were positive by PCR for C. jejuni/C. coli , but 27.6% were positive for non- jejuni/coli Campylobacter species. Sequencing of 16S rRNA from 53 of these non- jejuni/coli Campylobacter samples showed that it most closely matched the 16S rRNA of C. hyointestinalis subsp. lawsonii (56%), C. troglodytis (33%), C. upsaliensis (7.7%), and C. jejuni/C. coli (2.6%). Campylobacter -negative stool spiked with each of the above-mentioned Campylobacter species revealed reactivity with EIA. PCR detection of Campylobacter species was strongly associated with diarrhea in Peru (odds ratio [OR] = 3.66, P < 0.001) but not in Tanzania (OR = 1.56, P = 0.24) or Bangladesh (OR = 1.13, P = 0.75). According to PCR, Campylobacter jejuni/C. coli infections represented less than half of all infections with Campylobacter species. In sum, in infants in developing country settings, the ProSpecT EIA and PCR for Campylobacter reveal extremely high rates of positivity. We propose the use of PCR because it retains high sensitivity, can ascertain burden, and can distinguish between Campylobacter infections at the species level.

Etiologic studies of diarrhea are limited by uneven diagnostic methods and frequent asymptomatic detection of enteropathogens. Polymerase chain reaction-based stool pathogen quantification may help distinguish clinically significant infections. We performed a nested case-control study of diarrhea in infants from a community-based birth cohort in Tanzania. We tested 71 diarrheal samples and pre-diarrheal matched controls with a laboratory-developed TaqMan Array Card for 19 enteropathogens. With qualitative detection, no pathogens were significantly associated with diarrhea. When pathogen quantity was considered, rotavirus (odds ratio [OR] = 2.70 per log10 increase, P < 0.001), astrovirus (OR = 1.49, P = 0.01), and Shigella/enteroinvasive Escherichia coli (OR = 1.47, P = 0.04) were associated with diarrhea. Enterotoxigenic E. coli (0.15 SD decline in length-for-age z score after 3 months per log10 increase, P < 0.001) and Campylobacter jejuni/C. coli (0.11 SD decline, P = 0.003) in pre-diarrheal stools were associated with poor linear growth. Quantitative analysis can help refine the association between enteropathogens and disease in endemic settings.

Background Several viruses can cause diarrheal disease, a leading cause of morbidity and mortality worldwide. Existing diagnostic methods include ELISA and nucleic acid amplification, usually performed individually. Objectives (1) To develop a multiplexed assay for simultaneous detection of major enteric viral pathogens. (2) Quantitation of viral load by normalizing with an extrinsic control. Study design A simple protocol combining a one-step multiplex reverse transcription-polymerase chain reaction (RT-PCR) with microsphere-based fluorescence detection was developed for norovirus GI and GII, rotavirus, astrovirus, sapovirus, and adenovirus. An extrinsic control, bacteriophage MS2, was spiked into each fecal sample before nucleic acid extraction to normalize between samples for the efficiency of nucleic acid extraction and amplification. Results The fluorescent results were quantitative and nearly as sensitive as the corresponding singleplex real time RT-PCR (qRT-PCR) assay on analytic samples. Upon testing 229 fecal samples from inpatients with diarrhea in Tanzania the assay yielded between 88% and 100% sensitivity and specificity for all analytes. The difference in fluorescence intensities of MS2 between samples indicated variable extraction efficiency and was used to better refine the viral load of each specimen. Conclusions This one-step nucleic acid-based assay enables rapid, sensitive and specific detection of the major viral causes of gastroenteritis. The quantitation yielded by the assay is informative for clinical research particularly in the context of mixed infections.

Background Largely due to the lack of diagnostic reagents, the prevalence and clinical presentation of cryptococcal meningitis in Tanzania is poorly understood. This in turn is limiting the impact of increased fluconazole availability. Methods We evaluated a cohort of 149 consecutive HIV-infected adult inpatients presenting with headache or altered mental status for clinical features, CD4 count, cryptococcal infection, and outcome. Cryptococcal meningitis was diagnosed via India ink and latex agglutination assay of CSF (n = 24 and 40 positive, respectively). Associations between cryptococcal meningitis and clinical features were evaluated by t-test. The sensitivity, specificity, and positive likelihood ratio of such features were determined. Results Cryptococcal meningitis was associated with confusion, social withdrawal, seizures, fever, tachycardia, meningismus, oral candidiasis, and low Glasgow coma scales and CD4 count. CD4 count < 100/μl provided the highest sensitivity for the diagnosis (93%), coma (Glasgow coma scale ≤ 8) provided the highest specificity (84%), and the combination provided the highest positive likelihood ratio (3.8). All cryptococcal meningitis patients were initiated on 800 milligrams of fluconazole daily and 50% survived to discharge, however no clinical or laboratory findings correlated with prognosis. Conclusion Cryptococcal meningitis is common among Tanzanian HIV inpatients presenting with headache or altered mental status. Purely clinical features are insensitive for establishing the diagnosis or prognosis. We advocate expanding laboratory capacity for cryptococcal antigen testing to maximize survival.