Updates
By Carol A. Kemper, MD, FACP, Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases; Santa Clara Valley Medical Center, Section Editor, Updates; Section Editor, HIV, is Associate Editor for Infectious Disease Alert.
I've Got the Feline Flu
Source: ProMED-mail post November 5, 2009; www.promedmail.org; www.avma.org/public_health/influenza/new_virus.
Various strains of human influenza virus can infect other mammalian species. Strains of H1N1 have been shown to cause respiratory illness in pigs, birds, and a group of family ferrets in Oregon. The American Veterinary Medical Association (AVMA) reports the first case of H1N1 influenza illness in a family cat. Two of three human members of the household were ill with flu-like symptoms before the 13-year-old cat developed respiratory symptoms and was taken to the Iowa State University's College of Veterinary Medicine for care. Nasal swab specimens were positive for 2009 influenza A (H1N1) virus. The WHO emphasizes that H1N1 infection in pets are "isolated events and pose no risk to human health." The Iowa DPH stated this event should not be too surprising, as other human influenza viruses have infected domestic cats.
The AVMA has posted and a FAQ sheet on their website for pet owners, warning that family pets can get the flu, and suggest that pets be protected from ill family members.
Bacterial Co-infection in H1N1 Influenza
Source: Bacterial Coinfections in lung tissue specimens from fatal cases of 2009 pandemic influenza A (H1N1) - US, May-August 2009. MMWR. 2009;58.
Data early on in the pandemic influenza outbreak suggested that most severely ill patients with Influenza A were not suffering from bacterial co-infection. An initial MMWR report found no evidence of bacterial superinfection in 30 patients hospitalized in April-May 2009 with confirmed H1N1 in California,1 although 15 of 25 (60%) with chest radiographs had pulmonary infiltrates. Two-thirds had multilobar infiltrates and four patients required mechanical ventilation. A second report in the MMWR this summer described an additional 10 patients with H1N1 influenza requiring critical care in Michigan lacking evidence of bacterial pneumonia.2
These reports may have been misleading, insomuch as causative agents of pneumonia are difficult to identify, even under optimal circumstances. Newer data, based on autopsy specimens, suggest that nearly one-third of patients with fatal H1N1 illness have evidence of super-infecting bacterial pneumonia. Respiratory specimens (lung, trachea, and large-airway specimens) collected at autopsy from 77 patients with laboratory-confirmed fatal H1N1 infection were evaluated for evidence of bacterial infection. This included tissues stains, immunohistochemical antibody testing for various bacterial pathogens (including antibodies to S. pneumoniae, S. pyogenes, S. aureus, H. influenza but not legionella spp.), and PCR-based assays to further characterize streptococcal and pneumococcal infection. H1N1 infection was confirmed in 41 of the patients before death and identified in 36 patients post-mortem.
Of the 77 fatal cases of H1N1 infection submitted for analysis, 22 (29%) had histopathological, immunohistochemical, and molecular evidence of bacterial pneumonia.
Streptococcus pneumoniae was the most frequently identified pathogen, occurring in 10 persons (13%), followed by S. aureus (9.1%), S. pyogenes (7.8%), S. mitis (2.6%), and H. influenza (1.3%). Multiple bacterial pathogens were found in four patients (5%). The mean age at death was 31 (range, two months to 56 years), and half were male. The median duration of illness, available for 17 of the patients, was six days (range, 1 to 25 days). Fourteen had received some kind of medical care, at least seven had received antibiotics, and eight had been hospitalized. In 21 patients for whom this kind of information was available, 16 had significant underlying medical conditions known to increase the risk for severe influenza infection (five were described as obese, two each with diabetes, asthma, and Down Syndrome, and one with HIV infection).
The presence of bacterial pneumonia in nearly one-third of patients with fatal H1N1 infection should be viewed as a minimum estimate of the risk of bacterial superinfection in such patients. Even with the best techniques, super-infecting bacterial pneumonia in patients with viral pneumonia or ARDS may be difficult to confirm. Based on this data, empiric antibacterial therapy should be considered for critically ill patients with influenza, at least until their respiratory status has stabilized or improved. An agent with activity against MRSA should be considered, especially in persons at risk.
References
- CDC. Hospitalized patients with novel influenza A (H1N1) virus infection — California, April-May, 2009. MMWR. 2009;58:749-752.
- CDC. Intensive-care patients with severe novel influenza A (H1N1) virus infection — Michigan, June 2009. MMWR. 2009;58:749-752.
Just Say "No" to N95s?
The debate over the use of N95s respirator masks when caring for persons with influenza has become contentious in our area, although it was obvious to most ID specialists and infection-control personnel that the unusually hyped-up requirements for PPE with this flu season were not evidence-based and added to the anxiety of health care workers caring for ill patients. Clinical and hospital staff have filed reports with Cal-OSHA reporting inadequate workplace precautions and a lack of access to respirators (these are some of the same nursing staff who refuse influenza vaccination every year). Despite CDC and Cal-OSHA recommendations for use of respirators in caring for patients with the flu, inadequate supplies of masks have been made available, and we've run out of the smaller masks at our hospital (which created problems when an infectious TB patient was recently admitted).
The initial CDC recommendations for the use of respirators with this flu season appear to have been based on early reports of higher than expected mortality (which were erroneous), the unknown potential for mutation to a more virulent strain, and the results of a single study, initially presented at ICAAC in September 2009,1 suggesting that N95 masks provided superior protection against transmission of flu virus relative to regular surgical masks (although later data, presented at IDSA in October, found no statistically significant benefit2). These initially confusing results stemmed from an investigation of 1,936 health care workers from 24 hospitals in Beijing who were randomly assigned to N95 masks (fit tested), N95 masks (not fit tested), and regular surgical masks for four weeks, and then followed for five weeks. Preliminary data suggest that N95s were 56% protective against confirmed clinical respiratory illness and 70% protective against confirmed influenza. Regular surgical masks did not appear to offer protection. Subsequent analysis and adjustment for clustering and multiple comparisons failed to confirm a benefit for the use of N95s vs. regular masks.
These data were further supported by Loeb at al., published in JAMA in October 2009.3 This non-inferiority trial compared N95s vs. regular surgical masks in 446 nurses in medical, surgical, and emergency units in eight Toronto hospitals during the 2008-2009 influenza season. Staff were randomly assigned to either mask. The primary outcome was confirmation of influenza by PCR or by a four-fold increase in hemagglutinin titers. Confirmed influenza occurred in 50 nurses (23.6%) wearing surgical masks and 48 nurses (22.9%) in the N95 group (absolute risk difference, — 0.73%, with the lower confidence limit not meeting criteria for non-inferiority).
Interesting data demonstrating a lack of airborne transmission for H1N1 influenza virus was observed during an outbreak of Influenza A (H1N1) among an American tour group traveling to China in June 2009.4 A 40-year-old woman developed influenza-like illness, confirmed as H1N1, shortly before landing in China; her travel itinerary required three separate airflights and a tour bus (the kind where you cannot open the windows and 70% of the air is conditioned and recirculated). Several members of the tour group were quarantined, and everyone on the tour and on the airplanes was queried regarding the presence of ILI for the next two weeks. Ten additional cases of H1N1 were confirmed, including nine members of the tour group. The attack rate was higher for women than men (50% vs. 13%). Amazingly, of the 16 persons on the tour who had talked with the index case for at least two minutes, 56% developed influenza; if they had chatted for more than 10 minutes, the risk of infection was 5x greater. None of 14 members of the tour group who had not conversed with the index case became ill. Only one of 87 passengers on one of the flights, who was not on the tour group, but who had sat within two rows of the index case, developed influenza.
Just the act of chatting with the index case (as woman were obviously more wont to do) resulted in transmission of influenza virus through droplets. These data provide no evidence of airborne transmission of virus on the bus or on the airplanes. SHEA/IDSA/APIC have appealed to the Obama administration urging the White House to modify 2009 H1N1 guidelines for health care workers and to issue a moratorium on OSHA enforcement. Let's hope for a sensible response.
References
- MacIntyre C, et al. 49th ICAAC, September 15, 2009 (abstract K-1918b).
- The IDSA abstract, 47th IDSA, October 2009 (abstract 1247)
- Loeb M, et al. Surgical Mask vs N95 respirator for preventing influenza A among health care workers: A randomized trial. JAMA. 2009. (epub Occtober)
- Han Ke, et al. Lack of airborne transmission during outbreak of Pandemic (H1N1) 2009 among tour group members, China, June, 2009. Emerg Infect Dis. 2009.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content