Infectious Disease Consult

From the 66th Annual Brennemann Lectures, sponsored by the Los Angeles Pediatric Society

Wilbert H. Mason Jr,  MD, MPH, Professor of Clinical Pediatrics, Keck School of Medicine of the University of Southern California, and Head, Division of Infectious Disease, Children’s Hospital Los Angeles,

Educational Objectives

The goal of this program is to improve diagnosis of pediatric infectious diseases and management of influenza A (H1N1). After hearing and assimilating this program, the clinician will be better able to:

1.   Describe the mechanisms of action and advantages of nucleic acid-based molecular diagnostic tests.

2.   Begin earlier and more effective treatment of common pediatric infectious diseases using nucleic acid- and im­mune-based diagnostic methods.

3.   Effectively diagnose patients with seasonal influenza and pandemic influenza.

4.   Identify patients who are at increased risk of developing severe illness from influenza H1N1.

5.    Describe the safety profile and anticipated side effects of influenza vaccines, including the risk of developing Guillain-Barré syndrome.

Faculty Disclosure

In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and members of the plan­ning committee to disclose relevant financial relationships within the past 12 months that might create any personal con­flicts of interest. Any identified conflicts were resolved to ensure that this educational activity promotes quality in health care and not a proprietary business or commercial interest. For this program, the following has been disclosed: Dr. Mason is on the Speakers’ Bureaus of Merck and MedImmune. In his lecture, Dr. Mason presents information that is related to the off-label or investigational use of a therapy, product, or device.  The planning committee reported nothing to disclose.

Acknowledgements

Dr. Mason spoke in Anaheim, CA, at the 66th Brennemann Lectures, presented October 22-25, 2009, by the Los Angeles Pediatric Society. The Audio-Digest Foundation thanks Dr. Mason and the Los Angeles Pediatric Society for their coopera­tion in the production of this program.

Molecular and Immune-Based Diagnosis in Pediatric Infectious Disease

Diagnosis: serology  —  long turnaround time; IgM tests  —unreliable (many false positives); culture and staining  —   lack sensitivity; require ³2 or 3 days; subject to contamination; expensive; molecular diagnostics  —   greater sensi­tivity and specificity; faster turnaround time; result in shorter hospitalizations and more specific therapy; potential for lower cost of care, but currently expensive; personalized medicine  —  antibiotics selected not only on basis of susceptibility of organism, but also on genetic makeup of patient

Molecular Diagnostic Tests

Nonamplified nucleic acid (NA) probes: fragments of DNA or RNA attached to peptides; contain bases comple­mentary to DNA or RNA of target organism, enabling detection of nucleotide sequences that identify organism; probe labeled with reporter molecules; when probe binds to target, reporter molecules released, resulting in direct detection of pathogens in clinical specimens; since probes pathogen-specific, can identify organisms at any taxo­nomic level; low risk for contamination of samples; currently used for identifying Staphylococcus aureus, Pseudo­monas aeruginosa, mycobacteria, and Candida species; many available in multiplex systems with >1 probe

Target amplification: amplified NA methods using polymerase chain reaction (PCR); allows detection of even 1 or 2 target organisms; real-time (RT) PCR amplifies target DNA until measurable quantity obtained; multiplex systems can identify 3 to 5 targets; organisms currently identified include Streptococcus pyogenes, methicillin resistant S aureus (MRSA), Bordetella pertussis, Legionella pneumophila, Mycoplasma pneumoniae, Mycobacterium tuber­culosis, herpes simplex virus (HSV), cytomegalovirus (CMV), varicella zoster virus (VZV), Epstein-Barr virus (EBV), Aspergillus, and Pneumocystis jiroveci

Signal amplification: concentration of probe or target does not increase; increased analytical sensitivity comes from increasing signal molecules attached to target NA; currently used for identifying Neisseria gonorrhoeae and Chla­mydia trachomatis

Postamplification analyses: use products of RT-PCR to detect pathogens; after multiplex PCR amplification, targets incubated with custom-designed microbeads (Luminex) labeled with reporter molecules that identify organism; re­verse hybridization also available; currently used for identifying respiratory viruses, including H1N1 influenza, and Cryptococcus 

Clinical Applications

Pertussis: nasopharyngeal cultures highly insensitive because organism difficult to culture; direct fluorescent anti­body assays (DFA) 30% to 70% sensitive; PCR 4 times more sensitive, even after start of therapy; after 2 days of therapy, sensitivity of DFA 56% vs 89% for PCR; after 4 days of therapy sensitivity of DFA 0% vs 56% for PCR; NA test method of choice for identifying pertussis

Tuberculosis (TB): sputum smears 50% to 80% sensitive in adults; acid-fast bacteria (AFB) cultures 80% to 85% sensitive in adults; microbial culture 28% sensitive in children and take 3 to 6 wk; NA amplification tests  —  provide results in 24 to 48 hr; positive predictive value >95% in patients with smear-positive Mycobacterium tuberculosis (MTB); confirms MTB in 50% to 80% of patients with smear-negative disease; confirms MTB weeks earlier than culture; molecular beacon assay identifies multiple-drug resistant TB organisms; Centers for Disease Control and Prevention (CDC) recommends NA amplification for diagnosis of TB in all patients

Respiratory viruses and influenza: rapid viral test  —variable sensitivity; 60% to 90% for seasonal influenza, 10% to 70% for H1N1 influenza; NA analysis  —distinguishes among type A, type B, seasonal, H1N1, and pandemic H1N1 influenza and other respiratory viruses, eg, rhinovirus; in study of 101 specimens variably reported by direct antigen assay, NA assay correctly identified 99 of 101; important for treatment since different strains have different susceptibilities to antiviral agents

Enteroviral infections: 75,000 cases each year in United States; cause 80% to 90% of aseptic meningitis cases; over­lap between clinical and laboratory manifestations of bacterial and viral disease; sensitivity of viral culture 65% to 75%; culture results take weeks; enteroviral RT-PCR  —   takes <24 hr; sensitivity and specificity approach 100%; RT-PCR study  —  276 patients; those tested with enteroviral PCR had fewer additional tests (26% vs 72%); shorter courses of intravenous (IV) antibiotics (2.0 vs 3.5 days); shorter length of stay (42 vs 71.5 hr); more rapid discharge from hospital (5.2 vs 27.4 hr)

Immune-Based Tests

Tuberculosis: children with latent tuberculosis at high risk for developing active disease; risk 50% at age <1 yr, 20% at age <2 yr; at age >2 yr, risk 5% during subsequent 2 yr and 5% thereafter (lifetime risk of 10%); skin test   —    sensitivity in young children unknown; cross-reactive with other mycobacterial organisms; may be confounded by positive response after bacillus Calmette-Guérin vaccination (BCG) or by anergy; interferon-¡ (IFN-¡) release assay  —commercially available in United States (QuantiFERON-TB GOLD) and in Europe (ELISpot); tests do not distinguish active from latent TB; aliquots of heparinized whole blood incubated with test and control antigens for 16 to 24 hr; must be incubated <12 hr after collection; IFN-¡ measured by enzyme-linked immunoassay (ELISA); sensitive and specific; no cross reactivity with other Mycobacterium species; does not stimulate IFN-¡ production in cells sensitized by BCG or Mycobacterium avium; more sensitive in adults than in children; not recommended for young children

Emerging Infectious Disease in Pediatrics:
Influenza A (H1N1) Influenza

Viral nomenclature: includes type and place of isolation; strain designation; year of isolation; subtype based on type of hemagglutinin and neuraminidase; hemagglutinin  —found on surface of virus; responsible for attachment, pene­tration, and fusion of viral lysosome to host membrane; neuraminidase  —  cleaves terminal sialic acid residues on virion particles, which allows cell to infect other cells; prevents clumping; may facilitate release of virus

Pandemics: occur after major shift in antigenicity of virus; pandemic influenza always type A; population has no im­munity based on previous infection; current H1N1 virus includes reassortment of genetic material from avian, hu­man, and 2 swine species; virulence and transmissibility varies from pandemic to pandemic

Seasonal vs pandemic flu: seasonal flu  —   respiratory illness transmitted from person to person; some natural immu­nity; healthy adults usually not at risk; health system meets needs of public; pandemic flu  —  virulent human flu re­sulting in global outbreak; little natural immunity; occurs following major shift in antigenicity of virus; may include type A virus from humans, birds, and pigs; occurs every 10 to 40 yr; healthy people may be at increased risk; health system may be overwhelmed; designation as pandemic depends on how much human-to-human trans­mission occurs and on geographic distribution, not on virulence

Phases of pandemic: from World Health Organization (WHO); phase 1  —  animal influenza but no human disease; phase 2  —  animal influenza that has occasionally caused human disease; phase 3  —  sporadic disease with possible human to human transmission; phase 4  —  verified human to human transmission; phase 5  —  human to human spread in 2 countries and 1 region; phase 6  —  global pandemic under way; for influenza H1N1, pandemic status achieved in June 2009

Transmission: via large droplets of respiratory secretions; environmental surfaces (fomites); possibly spread by small, aerosolized droplets

Natural history: incubation period  —  for children and adults, 1 to 4 days (7 days maximum); infectiousness  —  1 day before onset of symptoms to 5 days after (adults); 4 days before symptoms to 10 days after (children); virus carried into all populations by children

Clinical findings: prostrating disease; children  —  abrupt onset of fever; cough; rhinorrhea; gastrointestinal symp­toms; otitis media; adults  —  abrupt onset of fever; myalgia; headache; malaise; case describer  —  fever >37.8°C and cough

Novel Influenza A (H1N1)

Background: first identified in 2 infants in California (April 2009); at present, United States experiencing wide­spread disease; laboratory confirmed H1N1  —  concentrated in youth; 0 to 4 yr of age (11%); 5 to 24 yr of age (50%); hospitalizations  —   preponderance in children, youth, and young adults; deaths  —  concentrated in persons <50 yr of age; underlying conditions predisposing to serious disease  —  asthma; chronic obstructive pulmonary dis­ease; diabetes; chronic cardiovascular disease; smoking; immunocompromise; obesity; neurodegenerative or neu­rodevelopmental disease, particularly those that impair clearance of respiratory secretions

Laboratory diagnosis: rapid influenza diagnostic tests (RIDT)  —  low reliability; accuracy 40% to 69% for pandemic flu, somewhat higher for seasonal flu; negative predictive value 32%; CDC recommends against using negative RIDT for management of patients, use clinical impression; RT-PCR  —  95% to 100% accurate for pandemic influ­enza; sensitivity and specificity 80% to 100%

Therapeutic guidelines: clinical indications for initiating therapy in young children  —   fast or troubled breathing; bluish or gray skin color; not drinking enough fluids; severe or persistent vomiting; not waking or interacting; very irritable; flu-like symptoms improve then return with fever and worse cough (sign of bacterial superinfection)

Viral susceptibility: important to specifically identify virus because of differences in susceptibility; oseltamivir  —  99% active against most viruses but seasonal influenza A mostly resistant to oseltamivir; shortens duration of symptoms in adults by 1.3 days and in children by 1.5 days; zanamivir  —active against all strains, including sea­sonal influenza A and B; shortens duration of symptoms by 1 to 2 days

Treatment recommendations: clinical judgment crucial because of diagnostic difficulties; indications for antiviral therapy  —  severe underlying illness and suspected or confirmed influenza (particularly hospitalized patients); sus­pected or confirmed influenza in individuals with risk factors for severe illness; predictors of hospitalization in children  —  age (<2 yr); high-risk medical conditions (eg, cardiac disease, neurologic and neuromuscular disease, respiratory tract disease); evidence of lower respiratory tract disease should prompt more careful evaluation; risk factors for severe illness  —  children <5 yr of age (especially <2 yr of age); age > 65 yr; pregnancy (pregnant women in third trimester have 6-fold greater chance of death from influenza); persons <19 yr of age receiving long-term as­pirin therapy; persons with chronic pulmonary conditions (especially asthma); persons with cardiovascular, renal, hepatic, hematologic, metabolic (including diabetes), or neuromuscular disorders; immunosuppression (due to medications or HIV); thus far, »70% of persons hospitalized with H1N1 have had recognized underlying condition (60% of children, 80% of adults); healthy persons who develop influenza and those who appear to be recovering from influenza do not need treatment

Infection control: frequent hand washing; coughing into elbow or tissue; delay return to work or school until 24 hr after free of fever without antipyretics; same precautions for health care workers, except for those working in pro­tected environment unit (eg, bone marrow transplant unit; return to work after 7 days); use of personal protective equipment  —  droplet precaution (assume droplet travels 6 ft); masking of patient and caregiver; standard contact precautions (gown, gloves, and eye protection); study found influenza aerosol in emergency department room air; study from China reported N95 mask more effective than surgical masks against H1N1 virus; recent JAMA article found no difference between masks in seasonal influenza; CDC recommends use of N95 mask on entering room of patient with H1N1 influenza; shortage of N95 masks drives practice variances

Immunization: seasonal and influenza H1N1 vaccines strongly recommended; H1N1 vaccine prioritized based on public health concerns and risk factors for disease; safety of both vaccines anticipated; surveillance for side effects ongoing; priority groups for H1N1 vaccine  —  health care and emergency medical service workers; children <6 mo to 18 yr of age (priority given to those with comorbid conditions); household and caregivers of children <6 mo; adults 18 to 24 yr; pregnant women; adults 24 to 64 with underlying medical conditions

Safety: influenza not transmitted by vaccines; live attenuated influenza vaccine  —  associated with nasal congestion, sore throat, cough, and malaise; wheezing in young children; inactivated vaccine  —  associated with arm soreness, fever, malaise, and myalgia; Guillain-Barré syndrome (GBS)  — annual incidence of GBS in United States 10 to 20 cases per 1 million adults; Campylobacter infection and upper respiratory infection most common predisposing ill­nesses; 1976 vaccine associated with 1 additional case per 100,000 persons immunized (cause never determined); subsequent flu seasons have reported no increase or slight increase in incidence of GBS; if GBS is side effect of vaccine, risk very low; due to morbidity and mortality of H1N1 influenza, benefits outweigh risks; pneumonia  —  nearly one-third of flu-related deaths due to superimposed pneumonia; confirm patients immunization with pneu­mococcal vaccine; prophylaxis  —  limit use; CDC moving away from advising prophylaxis of at-risk patients and recommending waiting until early signs of disease seen before starting treatment; resistance seen mostly in those who received prophylaxis or unusually long course of oseltamivir

Suggested Reading

Fiore AE et al: Seasonal influenza vaccines. Curr Top Microbiol Immunol 333:43, 2009; Ginocchio CC et al: Likelihood that an unsubtypeable influenza A virus result obtained with the Luminex xTAG respiratory virus panel is indicative of in­fection with novel A/H1N1 (swine-like) influenza virus. J Clin Micro 47:2347, 2009; Glezen WP: Modifying clinical prac­tices to manage influenza in children effectively. Pediatr Infect Dis J 27:738, 2008; Landry ML et al: Rapid enterovirus RNA detection in clinical specimens by using nucleic acid sequence-based amplification. J Clin Microbiol 41:346, 2003; Lighter J et al: Latent tuberculosis diagnosis in children by using the QuantiFERON-TB Gold in-tube test. Pediatrics 123; 30, 2009; Lodha R et al: Newer diagnostic modalities for tuberculosis. Indian J Pediatr 71:221, 2004; Nicol MP et al: Comparison of T-SPOT.TB assay and tuberculin skin test for the evaluation of young children at high risk for tuberculosis in a community setting. Pediatrics 123:38, 2009; Nissen MD et al: Rapid diagnosis in pediatric infectious diseases: the past, the present and the future.  Pediatr Infect Dis J 21:605, 2002; Ramers C et al: Impact of a diagnostic cerebrospinal fluid enterovirus polymerase chain reaction test on patient management. JAMA 283:2680, 2000; Scalera NM et al: The first pandemic of the 21st century: a review of the 2009 pandemic variant influenza A (H1N1) virus. Postgrad Med 121:43, 2009; Shun-Shin M et al: Neuraminidase inhibitors for treatment and prophylaxis of influenza in children: systemic review and meta-analysis of randomized controlled trials. BMJ 339:3172, 2009.