Question 19

College Answer

Diagnosis

Diagnosis of H1N1 is taken against background of pre-test probability (season, signs and symptoms of flu-like illness, possible exposure, other confirmed cases) and the sensitivity and specificity of laboratory test.

rRT-PCR is most sensitive and specific.

Rapid antigen tests and Immunofluorescent antibody testing are not specific for different flu A subtypes

Serology useful for identifying patients post infection

Confirmation of the diagnosis of H1N1 influenza A (CDC case definition) requires influenza-like illness with laboratory-confirmed H1N1 influenza A virus detection by real-time reverse transcriptase PCR or culture.

Treat as positive in interim if test results uncertain

Management Priorities

Arrange transfer to appropriate centre with combined ICU/obstetric care

Isolation, negative pressure room, contact precautions

Antiviral treatment: antiviral oseltamivir – important not to delay treatment in pregnancy

Obstetric input and counseling patient and partner.

Pregnancy increases the likelihood of the development of severe disease.

Early delivery likely either spontaneous or therapeutic so commence etamethasone/dexamethasone for foetal lung maturation

Supportive management: as indicated mechanical ventilation using lung protective strategies, vasopressor support if hypotensive etc.

Discussion

This question comes in the wake of the H1N1 pandemic, and may never appear again. Writing in mid-2015, one might expect that we are more likely to get an Ebola question. These pandemic questions usually appear about 18 months after the end of the outbreak, to lull the candidates into a false sense of security.

In summary:

Diagnosis of H1N1 influenza

• Rapid antigen tests range in sensitivity from 38.3% to 53.3% - thus, they dont actually excludeH1N1 - but they do confirm the diagnosis rapidly in a proportion of cases.
• Real time reverse transcriptase PCR (rRT-PCR)is the gold standard against which the rapid antigen tests are measured
• Diagnosis relies on the presence of a flu-like illness, as well as rRT-PCR confirmation.
  • The features of "flu-like illness" require respiratory symptoms and a history of fever (not necessarily a "documented" fever).

Management of H1N1 influenza

• ABC management - intubation and ventilation as needed, using lung-protective strategies
• Oseltamivir - though it has recently come under fire, its use may still contribute to survival in patients at greatest risk of death. And it seems vaguely safe in pregnancy.
• Isolation
• Airborne precautions
• O&G consultation
• Preparation of the foetus for delivery with corticosteroids
• Preparation for transfer to a large ICU

Vasoo, Shawn, Jane Stevens, and Kamaljit Singh. "Rapid antigen tests for diagnosis of pandemic (Swine) influenza A/H1N1." Clinical infectious diseases49.7 (2009): 1090-1093.

Balish, A., et al. "Evaluation of rapid influenza diagnostic tests for detection of novel influenza A (H1N1) virus-United States, 2009." Morbidity and Mortality Weekly Report 58.30 (2009): 826-829.

Gerrard, John, et al. "Clinical diagnostic criteria for isolating patients admitted to hospital with suspected pandemic influenza." The lancet 374.9702 (2009): 1673.

Dunstan, H. J., et al. "Pregnancy outcome following maternal use of zanamivir or oseltamivir during the 2009 influenza A/H1N1 pandemic: a national prospective surveillance study." BJOG: An International Journal of Obstetrics & Gynaecology 121.7 (2014): 901-906.

Jefferson T, Jones M, Doshi P, Spencer EA, Onakpoya I, Heneghan CJ. Oseltamivir for influenza in adults and children: systematic review of clinical study reports and summary of regulatory comments. BMJ 2014; 348: g2545