Table 7.

Clinical summary of lessons learned during the “herald wave” of the swine influenza (H1N1) pandemic

	Diagnostic Difficulties	Infection Control Problems	Severity Indicators
Laboratory Diagnostic Difficulties	Clinical Diagnostic Difficulties	Influenza Precautions (Droplet and Contact)	Laboratory Test Indicators
RIDTs • Rapid influenza A tests false negative ≥30% • Respiratory fluorescent antibody (FA) viral tests did not improve diagnostic yield over the rapid influenza A tests, and did not always correlate with RT-PCR H1N1 results RT-PCR • RT-PCR was done in rapid influenza A negative patients to confirm/rule out the laboratory diagnosis of swine influenza • RT-PCR testing was usually restricted causing major problems with initially/diagnosing influenza precautions • Later when RT-PCR became available, commonly, RT-PCR results were reported after 5–7 days • In some cases of clinically certain swine influenza, the RT-PCR was negative • Possible explanations include: - poor specimen sample - oropharyngeal secretions may be negative for RT-PCR swine influenza (H1N1) with lung specimens that are positive	•Definite (laboratory) diagnosis •Diagnosis was problematic (see laboratory diagnosis above) in admitted patients, differentiating ILI from swine influenza (H1N1) pneumonia • Clinical diagnosis rested on ruling out: • Bacterial CAPs, eg, Legionnaires' disease • Viral CAPs, eg, CMV, RSV, metapneumovirus • Cardiopulmonary disorders, eg, exacerbation of CAD, CHF, AECB •Probable (clinical) diagnosis Based on key clinical features in admitted adults with ILIs • Dry cough • temperature >102°F • Severe myalgias Based on non-specific laboratory testsa • Relative lymphopenia • Thrombocytopenia • Leukopenia (if with relative lymphopenia/ thrombocytopenia) • Elevated CPKs • CXR • clear/accentuated basilar lung marking • Bilateral patchy interstitial infiltrates/ARDS • Small unilateral/bilateral pleural effusion • No focal segmental/lobar (cavitary/non-cavitary) infiltrates	•Many patients not placed on influenza precautions because of negative RIDTs •Patients later determined to have probable/definite swine influenza (H1N1) were eventually placed on precautions resulting in extensive/labor intensive contact investigation of exposed health care workers, patients and visitors Duration of Precautions •Duration of H1N1 shedding in respiratory secretions remains unclear •After oseltamivir therapy, H1N1 shedding in respiratory secretions terminated by day #3	•Degree/duration of relative lymphopenia •Leukopenia (with relative lymphopenia/thrombocytopenia) •Profound/prolonged hypoxemia (A-a gradient >35) Demographic Indicators •Pregnancy •Obesity/diabetes mellitus •Young healthy adults (not the very young, elderly)

Swine Influenza (H1N1) Prophylaxis	Swine Influenza (H1N1) Therapy	Mimics of Swine Influenza (H1N1) Pneumonia	Complications of Swine Influenza (H1N1)
Prophylaxis	Therapy	Adults	Pulmonary
•Oseltamivir seemed to be effective •Resistance strains (rare but of concern)	Antiviral Interventions •Oseltamivir seemed effective in mild/moderately ill patients •Peramivir was useful in those unable to take/failed oseltamivir Interventions to Improve Oxygenation •Amantadine seemed to improve oxygenation in some •Ventilator support the single most important lifesaving intervention •In those unable to be oxygenated by ventilator, extracorporeal membrane oxygenation (ECMO) was life saving in some patients	•Influenza A (human seasonal) •Avian influenza (H5N1) •Legionnaires' disease •Adenoviruses •Cytomegalovirus (CMV) Children •Respiratory syncytial virus (RSV) •Metapneumovirus •Influenza B	•Viral pneumonia due to swine influenza (H1N1) •Respiratory failure •ARDs •Bacterial co-infections remained the exception rather than the rule •Main problem is the limited literature reporting “bacterial co-infections” was recognizing organisms from respiratory secretions/lung specimens represented colonization not infection (without appropriate clinical correlation) •Highest potential co-infections rates reported only 0–4% •Highest rates reported 24% in those given CAP antibiotics suggested many/most of these isolates representing colonization rather than true infection •Excluding the above single report, antibiotics for bacterial CAP complicating swine influenza (H1N1) pneumonia appeared to be unnecessary Extrapulmonary CNS •Encephalitis was rare Cardiac •Increased evidence of acute myocardial infarction in healthy young adults •Exacerbation of existing CAD/CHF •Myocarditis Other •Unexplained increase in incidence/severe or acute appendicitis •Unexplained increase in Legionnaires' Disease during the swine influenza (H1N1) pandemic •Rhabdomyositis

^aOtherwise unexplained.